Packaged White Light Emitting Device Comprising Photoluminescence Layered Structure

ABSTRACT

A light emitting device includes a Chip Scale Packaged (CSP) LED, the CSP LED including an LED chip that generates blue excitation light; and a photoluminescence layer that covers a light emitting face of the LED chip, wherein the photoluminescence layer comprises from 75 wt % to 100 wt % of a manganese-activated fluoride photoluminescence material of the total photoluminescence material content of the layer. The device/CSP LED can further include a further photoluminescence layer that covers the first photoluminescence and that includes a photoluminescence material that generates light with a peak emission wavelength from 500 nm to 650 nm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/379,272, filed Jul. 19, 2021 (now U.S. Pat. No. 11,631,792), which inturn is a bypass continuation-in-part of international PCT applicationNo. PCT/US2020/023095, filed Mar. 17, 2020 (publication no.WO2020190914), which in turn claims the benefit of priority to (i) U.S.provisional application No. 62/820,249, filed Mar. 18, 2019, entitled“PHOTOLUMINESCENCE LAYER LIGHT EMITTING DEVICE” and (ii) U.S.provisional application No. 62/886,317, filed Aug. 13, 2019, entitled“PACKAGED WHITE LIGHT EMITTING DEVICES COMPRISING PHOTOLUMINESCENCELAYERED STRUCTURE”, each of which are hereby incorporated by referencein their entirety.

FIELD OF THE INVENTION

Embodiments of the present invention are directed to packaged whitelight emitting devices comprising photoluminescence material layers andembodiments concerning packaged light emitting devices includingmanganese-activated fluoride photoluminescence materials. Moreparticularly, although not exclusively, embodiments of the presentinvention are directed to packaged white light emitting devices thatutilize Chip Scale Packaged (CSP) LEDs.

BACKGROUND OF THE INVENTION

Photoluminescence wavelength converted light emitting LEDs (“LEDs”)include one or more photoluminescence materials (typically inorganicphosphor materials), which absorb a portion of the excitation light(typically blue) emitted by the LED and re-emit light of a differentcolor (wavelength). Manganese-activated fluoride phosphors such asK₂SiF₆:Mn⁴⁺ (KSF), K₂TiF₆:Mn⁴⁺ (KTF), and K₂GeF₆:Mn⁴⁺ (KGF) have a verynarrow red spectrum (Full Width Half Maximum of less than 10 nm fortheir main emission line spectrum) which makes them highly desirable forattaining high color gamut (NT SC, DCI-P3, Rec2020) in displayapplications and for attaining a high General Color Rendering Index (CRIRa) in general lighting applications. FIG. 1 is a sectional view of aknown packaged white light emitting device that utilizes amanganese-activated fluoride phosphor material. Referring to FIG. 1 ,the packaged light emitting device 10 comprises a package 12 having acavity 14 that contains at least one LED die (chip) 16. The cavity 14 isfilled with a transparent optical encapsulant 18 having a mixture of amanganese-activated fluoride phosphor and yellow to green light emittingphosphor such as a garnet based phosphor material incorporated(dispersed) in the encapsulant.

While manganese-activated fluoride photoluminescence materials arehighly desirable for the above reasons, there are several drawbacks thatmake their widespread use challenging. First, the absorption capabilityof manganese-activated fluoride phosphors is substantially lower(typically about a tenth) than that of europium-activated red nitridephosphor materials (such as CASN) that are currently commonly used inphotoluminescence wavelength converted LEDs. Therefore, depending on theapplication, in order to achieve the same target color point, the usageamount of manganese-activated fluoride phosphors typically can be from 5to 20 times greater than the usage amount of a correspondingeuropium-activated red nitride phosphor. The increased amount ofphosphor usage significantly increases the cost of manufacture sincemanganese-activated fluoride phosphors are significantly more expensivethan europium-activated red nitride phosphors (at least five times moreexpensive). As a result of the higher usage and higher cost, use ofmanganese-activated fluoride red phosphors can be prohibitivelyexpensive for many applications. Moreover, since a very highphotoluminescence material loading in silicone is required to achievethe desired color point this can reduce the stability of the dispensingprocess making it difficult to reliably dispense in packaged devices.

Another problem with fluoride-based phosphor materials is that theyreadily react with water or moisture which causes damage to the dopantmanganese which leads to a reduction or loss of their photoluminescenceemission (i.e. quantum efficiency) of the phosphor. Moreover, thereaction of the fluoride-based compound with water can generate verycorrosive hydrofluoric acid that can react with LED packaging materialthereby leading to component failure.

The present invention intends to address and/or overcome the limitationsdiscussed above by presenting new designs and methods not hithertocontemplated nor possible by known constructions. More particularly,there is a need for a cost-effective light emitting device that utilizesless manganese-activated fluoride photoluminescence material, enables amore stable dispensing process during manufacture, and possesses anoptimized LED packaging design that may effectively isolate thefluoride-based photoluminescence material from metal wires, electrodes,lead frame materials, and any water/moisture in the surroundingenvironment.

SUMMARY OF THE INVENTION

Embodiments of the invention relate to packaged white light emittingdevices comprising a photoluminescence material layered structure. Moreparticularly, embodiments concern a white light emitting packagecomprising a first photoluminescence layer disposed adjacent to thesolid-state excitation source (LED) which, in terms of a totalphotoluminescence material content within the layer, contains a majoritywt % of manganese-activated fluoride photoluminescence material(phosphor), for example 75 wt % to 100 wt %. The devices furthercomprise a second photoluminescence layer disposed on the firstphotoluminescence layer containing photoluminescence material thatgenerate light in the green to red region (500 nm to 650 nm) part of thevisible spectrum. The inventors have discovered that by locating themanganese-activated fluoride photoluminescence material in an“individual layer” separate from the other photoluminescence materials,the amount of manganese-activated fluoride photoluminescence materialrequired to achieve a given color target can be reduced by as much as60%. In this patent specification, a packaged light emitting device isused to specify that the photoluminescence material layered structureconstitutes a part of the light emitting device package. This is to becontrasted with remote phosphor (photoluminescence) devices in which aphosphor component is provided “remotely” to the excitation source, thatis, in a physically spaced relationship and separated by an air gap.

According to an aspect of the invention, there is provided a white lightemitting package comprising: a solid-state excitation source forgenerating excitation light with a dominant wavelength in a range 440 nmto 470 nm; and a layered photoluminescence structure comprising: a firstphotoluminescence layer comprising from 75 wt % to 100 wt % amanganese-activated fluoride photoluminescence material of a totalphotoluminescence material content of the first photoluminescence layer,and a second photoluminescence layer comprising photoluminescencematerial for generating light with a peak emission wavelength in a rangefrom 500 nm to 650 nm; wherein the second photoluminescence layer isdisposed on the first photoluminescence layer, and wherein the firstphotoluminescence layer is disposed adjacent to the solid-stateexcitation source. It may be understood that the first photoluminescencelayer is in closer proximity to the solid-state excitation source thanthe second photoluminescence layer. It may be understood that “closerproximity” is used to define the spatial relationship of the first andsecond photoluminescence layers relative to the excitation source and isused to specify that the first photoluminescence layer is proximal (i.e.a proximal layer) to the excitation source, while the secondphotoluminescence layer is distal (i.e. a distal layer) to theexcitation source. Moreover, “closer proximity” means that there are noother photoluminescence materials in the light path between thesolid-state excitation source and the first photoluminescence layer,though there may be light transmissive layers or light transmissivelayers containing materials other than photoluminescence materials, forexample light diffusive/scattering materials. Light emitting devices inaccordance with the invention provide an effective solution to addressthe high usage of manganese-activated fluoride photoluminescencematerials in packaged light emitting devices. Providing themanganese-activated fluoride photoluminescence material as a respectivelayer, that in terms of a total photoluminescence content of the layer,the layer contains a majority (at least 75 wt % of the totalphotoluminescence material content of the layer) up to exclusivelyconsisting of (100 wt %) manganese-activated fluoride photoluminescencematerial, is found to significantly reduce the usage amount of themanganese-activated fluoride photoluminescence material within thedevice (a reduction of from about 25% to 60%).

Comparing with known constructions (FIG. 1 ), a conventional white lightemitting device comprises a single photoluminescence layer comprising amixture of a manganese-activated fluoride photoluminescence material andother (non-fluoride) photoluminescence materials (for example, a greenphosphor material, typically a garnet based phosphor material or a rednitride-based phosphor such as CASN). In such an arrangement themanganese-activated fluoride photoluminescence material and otherphotoluminescence material(s) have equal exposure to excitation light,for example blue excitation light. Since manganese-activated fluoridephotoluminescence materials have a much lower blue light absorptioncapability than other photoluminescence materials (for example,green/yellow garnet-based phosphors or red nitride phosphors), a greateramount of manganese-activated fluoride photoluminescence material isnecessary to convert enough blue light to the required red emission. Bycontrast, in the structure according to the invention, themanganese-activated fluoride photoluminescence material in its separaterespective layer is exposed to blue excitation light individually (thatis it is not competing with other photoluminescence materials); thus,more of the blue excitation light can be absorbed by themanganese-activated fluoride photoluminescence material and unconvertedblue excitation light can penetrate through to the secondphotoluminescence layer containing the other photoluminescencematerials. Advantageously, in this structure/light emitting device, themanganese-activated fluoride photoluminescence material can moreeffectively convert the blue excitation light to red emission withoutcompetition from other photoluminescence materials such as green/yellowor orange to red emitting photoluminescence materials for example.Therefore, the amount (usage) of a manganese-activated fluoridephotoluminescence material required to achieve a target color point canbe significantly reduced, up to 80%, compared with known arrangements ofa single-layer comprising a mixture of photoluminescence materials.Therefore, a major benefit of the white light emitting devices of theinvention is a substantial reduction in manufacturing cost of the device(i.e. package) as significantly less manganese-activated fluoridephotoluminescence material is required to attain a desired color pointof generated light.

A further advantage of light emitting devices in accordance with theinvention is that the provision of a second photoluminescence layerdisposed over the first photoluminescence layer is able to protect andisolate the manganese-activated fluoride photoluminescence material inthe first layer from direct contact with any water/moisture in thesurrounding environment. Such a multi-layer or two-layerphotoluminescence layered structure provides an effective solution toaddress the poor moisture reliability of manganese-activated fluoridephotoluminescence materials, as discussed above. Thus, the inclusion ofa second photoluminescence layer provides the benefit of improvedmoisture reliability to the light emitting device (i.e. LED package). Itmay be that the second photoluminescence material layer is in directcontact with the first photoluminescence layer. Direct contact improvesthe ability of the light to traverse the interface between the first andsecond photoluminescence layers due to the elimination of an airinterface.

Embodiments of the invention find particular utility to CSP (Chip ScalePackaged) LEDs. In this specification, a CSP LED is an LED flip chip(die) having one or more photoluminescence layers that cover one or moreof its light emitting faces (e.g. top and/or side light emitting faces).As is known, an LED flip chip die has electrodes on its base and a toplight emitting face that is free of electrodes, bond wires or otherpackaging materials. Preferably, the photoluminescence layer(s)comprising the manganese-activated fluoride photoluminescence materialis of a substantially uniform thickness and may be applied to theface(s) of the LED chip using, for example, an optical coupling layer.In the case where the manganese-activated fluoride photoluminescencematerial layer is deposited on only a top light emitting face of theflip chip, the manganese-activated fluoride photoluminescence materialis prevented from contacting metal electrodes or bonding wire andpackaging materials which might otherwise react with themanganese-activated fluoride photoluminescence material.

According to a first aspect of the invention, a light emitting devicecomprises: a Chip Scale Packaged (CSP) LED, said CSP LED comprising: anLED chip that generates blue excitation light; and a photoluminescencelayer that covers a light emitting face of the LED chip, wherein thephotoluminescence layer comprises from 75 wt % to 100 wt % of amanganese-activated fluoride photoluminescence material of the totalphotoluminescence material content of the layer. The photoluminescencelayer can comprise a substantially uniform thickness layer such as afilm comprising the manganese-activated fluoride photoluminescencematerial. The photoluminescence film can be manufactured by, forexample, extrusion, slot die coating or screen printing and the filmthen applied to at least the principle (top) light emitting face of theLED chip using, for example, a light transmissive medium such a siliconematerial. The photoluminescence layer comprising the manganese-activatedfluoride photoluminescence material may have a thickness from 20 μm to300 μm.

The device or CSP LED may comprise a further photoluminescence layercomprising photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm wherein the furtherphotoluminescence layer covers the photoluminescence layer comprisingthe manganese-activated fluoride photoluminescence material. Inembodiments where the further photoluminescence layer constitutes partof the device, the further photoluminescence layer can be constituted bysubstantially covering (or completely covering) the CSP LED with thefurther photoluminescence material by, for example, filling a cavity inwhich the CSP is mounted. In such embodiments, the furtherphotoluminescence layer may not be of uniform thickness. A benefit ofproviding the further photoluminescence layer as part of the device isthat since the further photoluminescence layer will have a greatervolume this can make it is easier to adjust the color temperature oflight generated by the device and easier to achieve a given colortemperature. Moreover, such arrangements allow the same CSP LED to beused to manufacture devices that generate different color temperaturesby changing the composition of the further photoluminescence layer. Inembodiments where the further photoluminescence layer constitutes a partof the CSP LED, the further photoluminescence layer may be directlyapplied to the photoluminescence layer comprising themanganese-activated fluoride photoluminescence material. In suchembodiments, the further photoluminescence layer may be of substantiallyuniform thickness. Such arrangements may have a fixed color temperature.

In some embodiments, the photoluminescence layer substantially coversonly a top light emitting face of the LED chip and a light reflectivematerial substantially covers the light emitting side faces of the LEDchip. The light reflective material can comprise a white material. Likethe further photoluminescence material, the light reflective materialmay comprise a part of the device or CSP LED. In embodiments where thelight reflective material constitutes part of the device, the lightreflective material can be constituted by a layer of light reflectivematerial that substantially covers the side faces of the LED chipwithout covering the photoluminescence layer by, for example, partiallyfilling a cavity in which the CSP LED(s) are mounted with the lighttransmissive material. In embodiments where the light reflectivematerial constitutes a part of the CSP LED, the light reflectivematerial may be directly applied to the side light emitting faces of theLED chip.

The light reflective material layer ensures that all blue lightgenerated by light emitting side faces of the LED chip passes into thephotoluminescence layer comprising a manganese-activated fluoridephotoluminescence material. This can be of particular benefit fordevices that are configured to generate lower CCT (warm light) light,for example up to 3000K, which require a greater proportion of red lightto achieve the desired color temperature. In this way, the inclusion ofa light reflective material that substantially covers the light emittingside faces of the LED chip can lessen a need of having to include moremanganese-activated fluoride photoluminescence material in thephotoluminescence layer to compensate for a “dilution” effect by coolerwhite created by the emission of blue light from the light emitting sidefaces of the LED chip. That is, the blue light emission from the lightemitting side faces of the LED chip can necessitate moremanganese-activated fluoride photoluminescence material usage in thephotoluminescence layer to generate the desired lower CCT (warm light)light, for example up to 3000K. A desired warmer color temperature canthus be attained without using more manganese-activated fluoridephotoluminescence material in the photoluminescence layer due to theinclusion of a light reflective material that substantially covers thelight emitting side faces of the LED chip. Since manganese-activatedfluoride photoluminescence material is significantly more expensive thanother types of photoluminescence materials (for example, green/yellowgarnet-based phosphors), reducing the amount of manganese-activatedfluoride photoluminescence material to attain a desired colortemperature (warm) by using a relatively inexpensive light reflectivematerial in this way provides a significant cost saving and makes theinvention more cost effective and economical to manufacture the lightemitting device.

A further benefit of having a light reflective material layer that atleast substantially covers the light emitting side faces of the LED chipis that this may lead to a more uniform color and uniform color overangle of emitted light.

The device or CSP LED can comprise a light transmissive material (layer)disposed between the light emitting side faces of the LED chip and thelight reflective material. The inclusion of such a light transmissivematerial layer can increase the amount of blue light generated by thelight emitting side faces of the LED chip that reaches thephotoluminescence layer. In such arrangements the photoluminescencelayer is preferably oversized such that it extends out from (project outfrom) the periphery of the top light emitting face and covers at leastthe light transmissive material. Typically, the light transmissivematerial can constitute a part of the CSP and can be formed, forexample, by bonding the top light emitting face of the LED chip to thephotoluminescence layer using a curable light transmissive liquid (suchas silicone) and selecting the quantity of light transmissive liquidsuch that the liquid forms a meniscus that extends up the light emittingside faces of the LED chip.

The device or CSP LED may comprise a further photoluminescence layercomprising photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm wherein the furtherphotoluminescence layer covers the photoluminescence layer comprisingthe manganese-activated fluoride photoluminescence material. Asdescribed herein, where the further photoluminescence layer constitutespart of the device, the further photoluminescence layer can beconstituted by completely covering the CSP LED with the furtherphotoluminescence material by for example filling a cavity in which theCSP is mounted. In such arrangements, the further photoluminescencelayer may not be of uniform thickness. A benefit of providing thefurther photoluminescence layer as part of the device is that since thelayer has a greater volume this can make it is easier to adjust thecolor temperature of light generated by the device and easier to achievea given color temperature. Moreover, such arrangements allow the sameCSP LED to be used to manufacture devices that generate different colortemperatures by changing the composition of the furtherphotoluminescence layer. Where the further photoluminescence layerconstitutes a part of the CSP LED the further photoluminescence layermay be directly applied to the photoluminescence layer comprising themanganese-activated fluoride photoluminescence material. In suchembodiments, the further photoluminescence layer may be of substantiallyuniform thickness. Such arrangements may have a fixed color temperature.

In some embodiments, the photoluminescence layer comprising themanganese-activated fluoride photoluminescence material covers all lightemitting faces of the LED chip. In such embodiments, thephotoluminescence layer can comprise a substantially uniform thicknessphotoluminescence layer such as a film. The photoluminescence layer/filmmay comprise a substantially conformal coating layer. The device or CSPLED may comprise a further photoluminescence layer comprisingphotoluminescence material that generates light with a peak emissionwavelength from 500 nm to 650 nm wherein the further photoluminescencelayer covers the photoluminescence layer comprising themanganese-activated fluoride photoluminescence material. As describedherein, where the further photoluminescence layer constitutes part ofthe device, the further photoluminescence layer can be constituted bycompletely covering the CSP LED with the further photoluminescencematerial by, for example, filling a cavity in which the CSP is mounted.In such embodiments, the further photoluminescence layer may not be ofuniform thickness. A benefit of providing the further photoluminescencelayer as part of the device is that since the layer has a greater volumethis can make it is easier to adjust the color temperature of lightgenerated by the device and easier to achieve a given color temperature.Moreover, such arrangements allow the same CSP LED to be used tomanufacture devices that generate different color temperatures bychanging the composition of the further photoluminescence layer. Inembodiments where the further photoluminescence layer constitutes a partof the CSP LED the further photoluminescence layer may be directlyapplied to the photoluminescence layer comprising themanganese-activated fluoride photoluminescence material. In suchembodiments the further photoluminescence layer may be of substantiallyuniform thickness and may comprise a substantially conformal coatinglayer.

In various embodiments, the photoluminescence layer comprising themanganese-activated fluoride photoluminescence material comprises from95 wt % to 100 wt % manganese-activated fluoride photoluminescencematerial of the total photoluminescence material content of thephotoluminescence layer.

The manganese-activated fluoride photoluminescence material layer cancomprise at least one of: K₂SiF₆:Mn⁴⁺, K₂TiF₆:Mn⁴⁺, and K₂GeF₆:Mn⁴⁺.

The manganese-activated fluoride photoluminescence material may compriseless than 45 wt % of a total photoluminescence material content of thedevice.

According to a second aspect, a white light emitting device comprises: aChip Scale Packaged (CSP) LED, said CSP LED comprising: an LED chip thatgenerates blue excitation light; a first photoluminescence layer thatcovers a light emitting face of the LED chip; and a secondphotoluminescence layer that covers the first photoluminescence layer;wherein the first photoluminescence layer comprises from 75 wt % to 100wt % of a manganese-activated fluoride photoluminescence material of thetotal photoluminescence material content of the first photoluminescencelayer; and wherein the second photoluminescence layer comprises aphotoluminescence material that generates light with a peak emissionwavelength from 500 nm to 650 nm.

One or both of the first and second photoluminescence layers can have auniform thickness comprise a substantially conformal coating layer.

One or both of the first and second photoluminescence layers may have athickness from 20 μm to 300 μm.

The first photoluminescence layer may comprise from 95 wt % to 100 wt %manganese-activated fluoride photoluminescence material of the totalphotoluminescence material content of the first photoluminescence layer.

The manganese-activated fluoride photoluminescence material layer cancomprise at least one of: K₂SiF₆:Mn⁴⁺, K₂TiF₆:Mn⁴⁺, and K₂GeF₆:Mn⁴⁺.

The manganese-activated fluoride photoluminescence material may compriseless than 45 wt % of a total photoluminescence material content of thedevice. In embodiments, the photoluminescence material in the secondphotoluminescence layer comprises a green to yellow photoluminescencematerial that generates light with a peak emission wavelength in a rangefrom 500 nm to 565 nm and/or an orange to red photoluminescence materialthat generates light with a peak emission wavelength in a range from 580nm to 650 nm.

According to an aspect, there is provided a Chip On Board (COB) whitelight emitting device comprises: a substrate; an array of CSP LEDsmounted on the substrate; and a further photoluminescence layer thatcovers the plurality of CSP LEDs, said further photoluminescence layercomprising photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm; and wherein the CSP LEDcomprises: an LED chip that generates blue excitation light; and aphotoluminescence layer that covers a light emitting face of the LEDchip, wherein the photoluminescence layer comprises from 75 wt % to 100wt % of a manganese-activated fluoride photoluminescence material of thetotal photoluminescence material content of the layer.

According to an aspect, there is contemplated a Chip On Board (COB)white light emitting device comprises: a substrate; an array of CSP LEDsmounted on the substrate; and a further photoluminescence layer thatcovers the plurality of CSP LEDs, said further photoluminescence layercomprising photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm, wherein the CSP LEDcomprises: an LED chip that generates blue excitation light; aphotoluminescence layer that covers a top light emitting face of the LEDchip; and a light reflective material that covers the light emittingside faces of the LED chip, wherein the photoluminescence layercomprises from 75 wt % to 100 wt % of a manganese-activated fluoridephotoluminescence material of the total photoluminescence materialcontent of the layer.

According to an aspect, there is envisaged a Chip On Board (COB) whitelight emitting device comprises: a substrate; an array of CSP LEDsmounted on the substrate; and a further photoluminescence layer thatcovers the array of CSP LEDs, said further photoluminescence layercomprising photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm, wherein the CSP LEDcomprises: an LED chip that generates blue excitation light; and aphotoluminescence layer that covers all light emitting faces of the LEDchip, wherein the photoluminescence layer comprises from 75 wt % to 100wt % of a manganese-activated fluoride photoluminescence material of thetotal photoluminescence material content of the layer.

Various embodiments of the invention also find utility in colortemperature tunable white light emitting devices.

According to an aspect, the present invention encompasses a colortunable Chip On Board (COB) white light emitting device comprises: asubstrate; a first array of CSP LEDs mounted on the substrate; a secondarray of blue LED chips that generate blue excitation light; and afurther photoluminescence layer that covers the first array of CSP LEDsand the second array of blue LED chips, said further photoluminescencelayer comprising photoluminescence material that generates light with apeak emission wavelength from 500 nm to 650 nm; and wherein the CSP LEDscomprise: an LED chip that generates blue excitation light; and aphotoluminescence layer that covers a light emitting face of the LEDchip, wherein the photoluminescence layer comprises from 75 wt % to 100wt % of a manganese-activated fluoride photoluminescence material of thetotal photoluminescence material content of the layer.

According to an aspect, there is provided a color tunable Chip On Board(COB) white light emitting device comprises: a substrate; a first arrayof CSP LEDs mounted on the substrate; a second array of blue LED chipsthat generate blue excitation light; and a further photoluminescencelayer that covers the first array of CSP LEDs and the second array ofblue LED chips, said further photoluminescence layer comprisingphotoluminescence material that generates light with a peak emissionwavelength from 500 nm to 650 nm; and wherein the CSP LED comprises: anLED chip that generates blue excitation light; a photoluminescence layerthat covers a top light emitting face of the LED chip; and a lightreflective material that covers the light emitting side faces of the LEDchip, wherein the photoluminescence layer comprises from 75 wt % to 100wt % of a manganese-activated fluoride photoluminescence material of thetotal photoluminescence material content of the layer.

According to an aspect, the present invention envisages a color tunableChip On Board (COB) white light emitting device comprises: a substrate;a first array of CSP LEDs mounted on the substrate; a second array ofblue LED chips that generate blue excitation light; and a furtherphotoluminescence layer that covers the first array of CSP LEDs and thesecond array of blue LED chips, said further photoluminescence layercomprising photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm; and wherein the CSP LEDscomprise: an LED chip that generates blue excitation light; and aphotoluminescence layer that covers all light emitting faces of the LEDchip, wherein the photoluminescence layer comprises from 75 wt % to 100wt % of a manganese-activated fluoride photoluminescence material of thetotal photoluminescence material content of the layer.

According to an aspect, the present invention encompasses a colortunable Chip On Board (COB) white light emitting device comprises: asubstrate; a first array of CSP LEDs mounted on the substrate; and asecond array of CSP LEDs mounted on the substrate; wherein CSP LEDs ofthe first array generate white light of a first color temperature andCSP LEDs of the second array generate white light of a second differentcolor temperature; and wherein CSP LEDs of the first and second arrayeach comprise: an LED chip that generates blue excitation light; aphotoluminescence layer that covers a top light emitting face of the LEDchip; a light reflective material that covers the light emitting sidefaces of the LED chip; and a further photoluminescence layer that coversthe photoluminescence layer; wherein the photoluminescence layercomprises from 75 wt % to 100 wt % of a manganese-activated fluoridephotoluminescence material of the total photoluminescence materialcontent of the layer and wherein the further photoluminescence layercomprises photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm.

According to an aspect, the present invention contemplates a colortunable Chip On Board (COB) white light emitting device that comprises:a substrate; a first array of CSP LEDs mounted on the substrate; and asecond array of CSP LEDs mounted on the substrate; wherein CSP LEDs ofthe first array generate white light of a first color temperature andCSP LEDs of the second array generate white light of a second differentcolor temperature; and wherein CSP LEDs of the first and second arrayeach comprise: an LED chip that generates blue excitation light; aphotoluminescence layer that covers all light emitting faces of the LEDchip; and a further photoluminescence layer that covers thephotoluminescence layer; wherein the photoluminescence layer comprisesfrom 75 wt % to 100 wt % of a manganese-activated fluoridephotoluminescence material of the total photoluminescence materialcontent of the layer and wherein the further photoluminescence layercomprises photoluminescence material that generates light with a peakemission wavelength from 500 nm to 650 nm.

In various aspects/embodiments of the invention, the photoluminescencematerial in the further photoluminescence layer can comprise a green toyellow photoluminescence material that generates light with a peakemission wavelength from 500 nm to 565 nm and/or an orange to redphotoluminescence material that generates light with a peak emissionwavelength from 580 nm to 650 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 is a sectional view of a known white light emitting device thatutilizes manganese-activated fluoride photoluminescence materials;

FIG. 2 is a sectional view of a packaged white light emitting device inaccordance with an embodiment of the invention;

FIG. 3 is a sectional view of a light emitting device in accordance withan embodiment of the invention;

FIG. 4 is a sectional view of a light emitting device in accordance withan embodiment of the invention;

FIGS. 5A to 5H are sectional views of light emitting devices inaccordance with an embodiment of the invention that utilize CSP (ChipScale Packaged) LEDs;

FIGS. 6A and 6B are respectively a plan view and cross sectional sideview through A-A a COB (Chip On Board) white light emitting device inaccordance with an embodiment of the invention;

FIG. 7 is a sectional view of a COB (Chip On Board) white light emittingdevice in accordance with an embodiment of the invention;

FIGS. 8A to 8F are cross sectional side views of COB (Chip On Board)white light emitting device in accordance with an embodiment of theinvention that utilize CSP (Chip Scale Packaged) LEDs;

FIGS. 9A to 9D are sectional views of Chip Scale Packaged (CSP) whitelight emitting devices in accordance with embodiments of the invention;

FIGS. 9E to 9K illustrate a method of manufacture of the Chip ScalePackaged (CSP) white light emitting device of FIG. 9D;

FIGS. 9L and 9M are sectional views of Chip Scale Packaged (CSP) whitelight emitting devices in accordance with embodiments of the invention;

FIGS. 9N to 9T illustrate a method of manufacture of the Chip ScalePackaged (CSP) white light emitting device of FIG. 9M;

FIG. 10 shows reliability data, relative intensity versus time, fordevices operated under accelerated testing conditions 85° C./85% RH for(i) a known 2700 K light emitting device (Com. 1) and (ii) a 2700K lightemitting device (Dev. 1) according to some embodiments;

FIGS. 11A to 11E are cross sectional side views of color tunable whitelight emitting devices in accordance with embodiments of the inventionthat utilize CSP (Chip Scale Packaged) LEDs; and

FIGS. 12A to 12E are cross sectional side views of COB (Chip On Board)color tunable white light emitting devices in accordance withembodiments of the invention that utilize CSP (Chip Scale Packaged)LEDs.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings, which are provided as illustrativeexamples of the invention so as to enable those skilled in the art topractice the invention. Notably, the figures and examples below are notmeant to limit the scope of the present invention to a singleembodiment, but other embodiments are possible by way of interchange ofsome or all of the described or illustrated elements. Moreover, wherecertain elements of the present invention can be partially or fullyimplemented using known components, only those portions of such knowncomponents that are necessary for an understanding of the presentinvention will be described, and detailed descriptions of other portionsof such known components will be omitted so as not to obscure theinvention. In the present specification, an embodiment showing asingular component should not be considered limiting; rather, theinvention is intended to encompass other embodiments including aplurality of the same component, and vice-versa, unless explicitlystated otherwise herein. Moreover, applicants do not intend for any termin the specification or claims to be ascribed an uncommon or specialmeaning unless explicitly set forth as such. Further, the presentinvention encompasses present and future known equivalents to the knowncomponents referred to herein by way of illustration.

Throughout this specification like reference numerals are used to denotelike parts. For all figures other than FIG. 1 , the reference numeral ispreceded by the figure number. For example, an LED chip 30 is referredto as 230 in FIG. 2, 330 in FIG. 3 and so forth.

Packaged White Light Emitting Devices

A packaged white light emitting device 220 in accordance with anembodiment of the invention will now be described with reference to FIG.2 which shows a sectional side view of the device 220.

The light emitting device 220 is a packaged-type device comprising, forexample an SMD (Surface Mount Device) package such as an SMD 2835 LEDpackage (lead frame) 222. The SMD package 222 comprises a rectangularbase 224 and side walls 226A, 226B extending upwardly from opposingedges of the rectangular base 224. The interior surfaces of the sidewalls 226A, 226B slope inwardly to their vertical axis and together withthe interior surface of the solid rectangular base 224 define a cavity228 in the shape of an inverted frustum of a pyramid.

In this embodiment, the cavity 228 can comprise three InGaN (IndiumGallium Nitride) blue (455 nm) LED dies (solid-state excitation sources)230, and a first photoluminescence layer 232 comprising amanganese-activated fluoride photoluminescence material fillingapproximately 70% of the cavity 228. The LED dies (chips) 230 can beserially connected and the rated driving condition is 100 mA, 9 V.

The first photoluminescence layer 232 contains a majority, at least 75wt %, of manganese-activated fluoride photoluminescence materialcompared with other photoluminescence materials that may be in thelayer. The first photoluminescence layer 232 may contain other materialssuch as light scattering particles or light diffusive material forexample. More particularly, in this embodiment, the firstphotoluminescence layer 32 only contains K₂SiF₆:Mn⁴⁺ (KSF), but notother types of photoluminescence materials. It will be appreciated,however, that other materials such as a light diffusive material can beadded into the manganese-activated fluoride photoluminescence materiallayer 232, but the amount of the other materials is typically no morethan 30% weight of the manganese-activated fluoride photoluminescencematerial layer 232. Further, in this embodiment, the firstphotoluminescence layer 232 is constituted by K₂SiF₆:Mn⁴⁺ incorporated(dispersed) in dimethyl silicone. The first photoluminescence layer 232is directly in contact with and adjacent the blue LED 230. There are noother photoluminescence materials or photoluminescence materialcontaining layers between the first photoluminescence layer 232 and theblue LED dies 230.

Comparing with known constructions, as shown for example in FIG. 1 , ina conventional single-layer light emitting device, the dispensingprocess during manufacture involves dispensing a mixture of amanganese-activated fluoride photoluminescence material and otherphotoluminescence material(s) (typically a green phosphor material)which have equal exposure to excitation light, for example blueexcitation light. Since a manganese-activated fluoride photoluminescencematerial may have a much lower blue light absorption capability thanother types of photoluminescence materials (for example, a green/yellowgarnet-based phosphors), a greater amount of manganese-activatedfluoride photoluminescence material is necessary to convert enough bluelight to the required red emission. By contrast, in the light emittingdevice 220 according to the invention, the manganese-activated fluoridephotoluminescence material in its separate individual layer 232 isexposed to blue excitation light individually; thus, more of the blueexcitation light from the blue LED dies (chips) 230 can be absorbed bythe manganese-activated fluoride photoluminescence material and theremaining blue excitation light can penetrate through to a secondphotoluminescence layer(s) 234 for instance. Advantageously, in thislight emitting device 220, the first photoluminescence layer 232 canmore effectively convert the blue excitation light to red emissionwithout competition from other types of photoluminescence materialspresent in the second photoluminescence layer 234 for example.Therefore, the amount/usage of a manganese-activated fluoridephotoluminescence material required to achieve a target color point canbe significantly reduced compared with known arrangements of a singlelayer comprising a mixture of photoluminescence materials for instance.Therefore, a benefit of the photoluminescence light emitting device 220of the invention is a reduction in the manufacturing cost of the devicesince less (up to 60% less) manganese-activated fluoridephotoluminescence material is required to attain a desired color pointcompared with known single-layer devices.

In this embodiment, the cavity 228 also comprises a secondphotoluminescence layer 234 dispensed on top of the firstphotoluminescence layer 232 that fills the remaining 30% of the cavity228. In this embodiment, the second photoluminescence material layer 234comprises a cerium-activated yellow garnet phosphor having a generalcomposition Y₃(Al,Ga)₅O₁₂:Ce. It will be appreciated that the secondphotoluminescence layer typically comprises green or yellow phosphors orother minority orange red phosphors that work in conjunction with thefirst photoluminescence layer to create the desired white point.

In this way, the light emitting device 220 effectively is able toisolate the manganese-activated fluoride photoluminescence materialcontained (incorporated (dispersed)) within the first photoluminescencelayer 232 from direct contact with any water/moisture in the surroundingenvironment. Such a multi-layer or two-layer design of the lightemitting device 220 provides an effective solution to address the poormoisture reliability of manganese-activated fluoride photoluminescencematerials in known constructions. Thus, the inclusion of the secondphotoluminescence material layer 234 provides the benefit of improvedmoisture reliability to the light emitting device (i.e. LED package)220.

The first photoluminescence layer 232 is adjacent (in closer proximity)to the blue LED 230 than any other photoluminescence material layerincluding the second photoluminescence material layer 234; that is thefirst photoluminescence layer 232 is adjacent (proximal—i.e. a proximallayer) to the blue LED 230, while the second photoluminescence materiallayer 234 is distal (i.e. a distal layer) to the blue LED 230.

Referring now to FIG. 3 , there is shown a packaged white light emittingdevice 320 (white light emitting device package) formed according toanother embodiment of the invention. This embodiment differs from FIG. 2only in that the light emitting device 320 further comprises a lighttransmissive (transparent) passivation layer 336 disposed on the blueLED die(s) 330 before the first photoluminescence layer 332. In order tofully protect the first photoluminescence layer 332 from water/moisture,the clear passivation layer 336 is applied over the floor of the cavity328 and LED dies (chips) 330 as shown in FIG. 3 . In this embodiment,the passivation layer 336 can be a layer of dimethyl silicone. Thispassivation layer 336 also serves to isolate the bottom electrode (notshown) and blue LED dies 330 from the first photoluminescence layer 332.

Referring to FIG. 4 , there is shown a packaged white light emittingdevice 420 (white light emitting device package) formed according toanother embodiment of the invention. In this embodiment the firstphotoluminescence layer 432, containing the manganese-activated fluoridephotoluminescence material, comprises a coating layer disposed on andcovering an individual LED chip 430. As illustrated the firstphotoluminescence layer 432 can be generally hemispherical (dome-shaped)in form. Compared with the first photoluminescence layer 232 of thelight emitting device of FIG. 2 , the first photoluminescence layer 432is more uniform in thickness and this reduces the variation inexcitation light photon density received by the manganese-activatedfluoride photoluminescence material within different physical locationwithin the layer. Initial test data indicates that such an arrangementcan reduce manganese-activated fluoride photoluminescence material usageby up to 80% by weight compared with the known white light emittingdevices comprising a single photoluminescence layer (for example FIG. 1).

The white light emitting device 420 can be manufactured by firstlydepositing the first photoluminescence layer 432 onto the LED chip 430and then filling the cavity 428 with the other photoluminescencematerial to form the second photoluminescence layer 452.

Packaged White Light Emitting Devices Utilizing CSP LEDs

FIGS. 5A and 5B are sectional views of packaged light emitting device inaccordance with an embodiment of the invention that utilize CSP (ChipScale Packaged) LEDs. In the light emitting devices of FIGS. 5A and 5B,the first photoluminescence layer 532 comprises a substantially uniformthickness coating layer that is applied to at least the principle (top)light emitting face of the LED chip 530. LED chips with a layer (film)of phosphor on their light emitting faces are often referred to as CSP(Chip Scale Packaged) LEDs. As illustrated in FIG. 5A, the device 520comprises a CSP LED comprising an LED chip 530 having a uniformthickness first layer 532 applied to it top (principle) light emittingface only. As illustrated in FIG. 5B, the device 520 comprises a CSP LEDcomprising an LED chip 530 having a uniform thickness first layer 532that covers (applied to) the top light emitting face and four side lightemitting faces and can, as shown, be in the form of a conformal coating.

The light emitting devices of FIGS. 5A and 5B can be manufactured byfirst applying the first photoluminescence layer 532 to at least theprinciple light emitting face of the LED chip 530, for example using auniform thickness (typically 20 μm to 300 μm) photoluminescence filmcomprising the manganese-activated fluoride photoluminescence material.The LED chip 530 is then mounted to the base 524 of the package 522 andthe second photoluminescence layer 532 is then deposited so as to fillthe cavity 528 and cover LED chip 530.

FIG. 5C is a sectional view of a further packaged light emitting devicein accordance with an embodiment of the invention that utilizes CSPLEDs. In this embodiment, the CSP LED includes first and secondphotoluminescence layers 532, 534 comprising a coating layer applied toat least the principle (top) light emitting face of the LED chip 530. Asillustrated in FIG. 5C, the first and second photoluminescence layers532, 534 can be applied to the top light emitting and four side lightemitting faces and may be of uniform thickness and in the form of aconformal coating. As shown, the package cavity 528 may be filled with alight transmissive material (optical encapsulant) 538 such as a siliconematerial to provide environmental protection of the CSP LED. The lightemitting device of FIG. 5C can be manufactured by first manufacturingthe CSP LED by applying the first and second photoluminescence layers532, 534 to light emitting faces of the LED chip 530, for example usinga first uniform thickness photoluminescence film comprising themanganese-activated fluoride photoluminescence material and then using asecond uniform thickness photoluminescence film comprising the otherphotoluminescence materials. The manufactured CSP LED chip is thenmounted to the base 524 of the package 522 and a light reflectivematerial 542 dispensed into the cavity 528 around the CSP LED up to thelevel of the first photoluminescence layer 532. Finally, the secondphotoluminescence layer 534 is deposited so as to fill the cavity 528and cover LED chip 530.

FIGS. 5D to 5H are sectional views of packaged light emitting device inaccordance with an embodiment of the invention that utilize CSP (ChipScale Packaged) LEDs having photoluminescence material that covers thetop light emitting face of the LED chip 530 only and additionallyinclude a light reflective material (layer) 542 that at leastsubstantially covers the light emitting side faces of the LED chip. Thelight reflective material 542 can comprise a white material such as awhite silicone material or alike.

The light reflective material layer 542 ensures that all blue lightgenerated by light emitting side faces of the LED chip 530 passes intothe first photoluminescence layer 532 comprising a manganese-activatedfluoride photoluminescence material. This can be of particular benefitfor devices that are configured to generate lower CCT (warm light)light, for example up to 3000K, which require a greater proportion ofred light to achieve the desired color temperature. In this way, theinclusion of a light reflective material 542 that substantially coversthe light emitting side faces of the LED chip 530 can lessen a need ofhaving to include more manganese-activated fluoride photoluminescencematerial in the photoluminescence layer to compensate for a “dilution”effect by cooler white created by the emission of blue light from thelight emitting side faces of the LED chip. That is, the blue lightemission from the light emitting side faces of the LED chip cannecessitate more manganese-activated fluoride photoluminescence materialusage in the photoluminescence layer to generate the desired lower CCT(warm light) light, for example up to 3000K. A desired warmer colortemperature can thus be attained without using more manganese-activatedfluoride photoluminescence material in the photoluminescence layer dueto the inclusion of a light reflective material that substantiallycovers the light emitting side faces of the LED chip. Sincemanganese-activated fluoride photoluminescence material is significantlymore expensive than other types of photoluminescence materials (forexample, green/yellow garnet-based phosphors), reducing the amount ofmanganese-activated fluoride photoluminescence material to attain adesired color temperature (warm) by using a relatively inexpensive lightreflective material in this way provides a significant cost saving andmakes the invention more cost effective and economical to manufacturethe light emitting device.

A further benefit of having a light reflective material layer that atleast substantially covers the light emitting side faces of the LED chipis that this may lead to a more uniform color and uniform color overangle of emitted light.

As shown in FIG. 5D the light reflective material 542 comprises a layerof light reflective material 542 that fills the cavity 528 to a levelthat substantially covers the side faces of the LED chip withoutcovering the first photoluminescence layer 532, and in at least someembodiments the reflective material 542 may fill the cavity 528 to alevel that completely covers the side faces of the LED chip withoutcovering the first photoluminescence layer 532. That is, the layer oflight reflective material 542 fills the cavity 528 to a level that atleast covers the side faces of the LED chip without covering the firstphotoluminescence layer 532. Consequently, the light reflective material542 can be considered to constitute a part of the package 522 ratherthan the CSP LED. Optionally, as indicated in FIG. 5D, the CSP LED maycomprise a light transmissive layer 544 (indicated by a dashed line)such as a glass or polymer film that covers the first photoluminescencelayer 532. The second photoluminescence layer 534 fills the remainder ofthe cavity 528 and covers the first photoluminescence layer 532.

The light emitting device of FIG. 5D can be manufactured by firstmanufacturing the CSP LED by applying the first photoluminescence layer532 to the light emitting top face of the LED chip 530, for exampleapplying a uniform thickness photoluminescence film comprising themanganese-activated fluoride photoluminescence material to the LED chip.Optionally, the first photoluminescence layer 532 may be provided on alight transmissive substrate 544 (indicated by a dashed line) such as aglass substrate or light transmissive polymer film. Since the firstphotoluminescence layer 532 may be thin, a benefit ofdepositing/fabricating the photoluminescence layer on a substrate can beease of manufacture when manufacturing the first photoluminescence layeras a separate component and then applying this to the LED chip. Themanufactured CSP LED chip is mounted to the base 524 of the package 522and the cavity 528 filled with a light reflective material 542 to alevel that substantially/completely covers the side faces of the LEDchip 530 without covering the first photoluminescence layer 532 or lighttransmissive layer (substrate) when present. A further benefit of thelight transmissive layer (substrate) 544 can be ease of manufacture whenfiling the cavity with the light reflective material 542. Moreparticularly, inclusion of the light transmissive layer (substrate) 544effectively increases the thickness of the first photoluminescence layer532 thereby allowing for a greater margin of error when filling thecavity 528 with the light reflective material 542 to ensure that it isnot filled beyond a level that would otherwise obstruct the emission oflight from the first photoluminescence layer 532 or light transmissivelayer 544 (substrate) when present. In this way, since less accuracy isrequired to fill the cavity 528 with the light reflective material 542to the correct level, this eases the complexity of the manufacturingprocess thereby diminishing costs.

The light emitting devices 520 of FIG. 5E and FIG. 5F utilize a CSP LEDof FIG. 9C and FIG. 9L respectively and each CSP LED comprises a firstphotoluminescence layer 532 that covers the top light emitting face ofthe LED chip 530 and a light reflective material 542 that covers each ofthe four light emitting side faces. The light emitting devices 520 ofFIG. 5G and FIG. 5H utilize a CSP LED of FIG. 9E and FIG. 9Mrespectively and each CSP LED comprises a first photoluminescence layer532 that covers the top light emitting face of the LED chip 530, a lightreflective material 542 that covers the light emitting side faces, and asecond photoluminescence layer 534 that covers the firstphotoluminescence layer. The CSP LEDs of FIGS. 9D, 9E, 9L and 9M arefurther described below together with their method of manufacture.

The light emitting devices of FIGS. 5E and 5F can be manufactured byfirst manufacturing the CSP LEDs as described herein, mounting the CSPLED to the base 524 of the package 522, and then depositing the secondphotoluminescence layer 532 so as to fill the cavity 528 and cover LEDchip 530.

The light emitting devices of FIGS. 5G and 5H can be manufactured byfirst manufacturing the CSP LEDs as described herein, mounting the CSPLED to the base 524 of the package 522, and optionally then filling thecavity 528 with a light transmissive medium 538.

Compared with the light emitting devices of FIGS. 2 and 3 a uniformthickness coating layer can be preferable as it concentrates all of themanganese-activated fluoride photoluminescence material as close to theLED chip as possible and ensures that regardless of physical locationwithin the layer all of the manganese-activated fluoridephotoluminescence material receives exposure to substantially the sameexcitation light photon density. Such an arrangement can maximize thereduction in manganese-activated fluoride photoluminescence materialusage. Initial test data indicates that such an arrangement can reducemanganese-activated fluoride photoluminescence material usage by up to80% by weight compared with the known white light emitting devicescomprising a single photoluminescence layer (for example FIG. 1 ). Thedescribed two-layer light emitting device structure comprisingrespective first and second photoluminescence layers is not limited tosurface mount packaged devices. For instance, it can also be applied inChip On Board (COB) or Chip Scale Packaged (CSP) applications.

COB (Chip on Board) Packaged White Light Emitting Devices

With reference to FIGS. 6A and 6B, there is shown a plan view and across section side view through A-A (of FIG. 6A) of a COB light emittingdevice 620 in accordance with another embodiment of the invention. Thelight emitting device 620 has a circular shape; and, can as illustrated,comprise a circular substrate (board) 624 which is planar and diskshaped. The substrate typically comprises a circuit board such as aMetal Core Printed Circuit Board (MCPCB). Forming a COB arrangement, 7arrays (rows) of blue LED dies 630 are evenly distributed on thecircular substrate 624. The circular substrate 624 also comprises aboutits entire perimeter a peripheral (annular) wall 626 which encloses allthe arrays of blue LED dies (chips) 630 and in conjunction with thesubstrate 624 define a volume (cavity) 628.

A first photoluminescence layer 632 comprising a manganese-activatedfluoride photoluminescence material is deposited onto the circularsubstrate 624 and, in this embodiment, completely covers the array ofblue LEDs 630. Similarly, a second photoluminescence material layer 634comprising a cerium-activated yellow garnet phosphor having a generalcomposition Y₃(Al,Ga)₅O₁₂:Ce is deposited onto the firstphotoluminescence layer 632 comprising the manganese-activated fluoridephotoluminescence material. In this way, the first photoluminescencelayer 632 and the second photoluminescence layer 634 are locatedadjacent one another and also contained within the wall 626.

The light emitting device 620 functions and exhibits the same advantagesas discussed in relation the light emitting devices of FIGS. 2, 3, 4, 5Ato 5E for example. Hence, the statements made in relation to thesefigures apply equally to the embodiment of FIGS. 6A and 6B.

A method of manufacturing the light emitting device, for example,comprises the steps of: providing an array of blue LEDs; dispensing amanganese-activated fluoride photoluminescence material layer (firstphotoluminescence layer) at least over said array of blue LEDs; anddispensing a second photoluminescence material layer over saidmanganese-activated fluoride photoluminescence material layer to fillthe volume 628.

FIG. 7 is a sectional view of a COB white light emitting device inaccordance with an embodiment of the invention. Referring to FIG. 7 ,there is shown a COB packaged white light emitting device 720 (whitelight emitting device package) formed according to another embodiment ofthe invention. In this embodiment the first photoluminescence layer 732,containing the manganese-activated fluoride photoluminescence material,comprises a respective individual coating layer disposed on and coveringeach LED chips 730. As illustrated the first photoluminescence layer 732can be generally hemispherical (dome-shaped) in form. Compared with thefirst photoluminescence layer 632 of the light emitting device of FIGS.6A and 6B, the first photoluminescence layer 632 is more uniform inthickness and this reduces the variation in excitation light photondensity received by the manganese-activated fluoride photoluminescencematerial within different physical location within the layer. Initialtest data indicates that such an arrangement can reducemanganese-activated fluoride photoluminescence material usage by up to80% by weight compared with the known white light emitting devicescomprising a single photoluminescence layer (for example FIG. 1 ).

COB White Light Emitting Devices Utilizing CSP LEDs

FIGS. 8A to 8F are cross sectional side views COB (Chip On Board) whitelight emitting device in accordance with embodiments of the inventionthat utilize CSP (Chip Scale Packaged) LEDs.

In the COB light emitting devices of FIGS. 8A and 8B the firstphotoluminescence layer 832 may comprise a respective uniform thicknesscoating layer that is applied to at least the principle light emittingface of each LED die (chip). As described herein, LED chips with auniform thickness layer (film) of phosphor on their light emitting facesare often referred to as CSP (Chip Scale Packaged) LEDs. As illustratedin FIG. 8A each LED chip 830 has a uniform thickness layer applied to ittop (principle) light emitting face only. As illustrated in FIG. 8B eachLED chip 830 has a uniform thickness layer applied to the top lightemitting and four side light emitting faces and is in the form of aconformal coating. The COB light emitting devices of FIGS. 8A and 8B canbe manufactured by first applying the first photoluminescence layer 832to at least the principle light emitting face of each of the LED chips830, for example using a uniform thickness (typically 20 μm to 300 μm)photoluminescence film comprising the manganese-activated fluoridephotoluminescence material. The LED chips 830 are then mounted to thebase 824 and the second photoluminescence layer 832 then deposited overthe array of LED chips to fill the volume 828. Compared with the lightemitting devices of FIGS. 6A and 6B a uniform thickness firstphotoluminescence layer is preferred as it concentrates all of themanganese-activated fluoride photoluminescence material as close to theLED chip as possible and ensures that regardless of physical locationwithin the layer all of the manganese-activated fluoridephotoluminescence material receives exposure to substantially the sameexcitation light photon density. Initial test data indicates that suchan arrangement can reduce manganese-activated fluoride photoluminescencematerial usage by up to 80% by weight compared with the known whitelight emitting devices comprising a single photoluminescence layer (forexample FIG. 1 ).

FIGS. 8C to 8F are sectional views of further COB white light emittingdevices 820 in accordance with embodiments of the invention that utilizeCSP LEDs having photoluminescence material that covers the top lightemitting face of the LED chip 830 only and a light reflective material(layer) 842 that covers the light emitting side faces. The lightemitting devices 820 of FIG. 8C and FIG. 8D utilize a CSP LED of FIG. 9Cand FIG. 9L respectively and each comprise a first photoluminescencelayer 832 that covers the top light emitting face of the LED chip 830and a light reflective material 842 that covers each of the four lightemitting side faces. The light emitting devices 820 of FIG. 8E and FIG.8F utilize a CSP LED of FIG. 9E and FIG. 9M respectively and eachcomprise a first photoluminescence layer 832 that covers the top lightemitting face of the LED chip 830, a light reflective material 842 thatcovers the light emitting side faces, and a second photoluminescencelayer 834 that covers the first photoluminescence layer. The CSP LEDs ofFIGS. 9D, 9E, 9L and 9M are further described below together with theirmethod of manufacture.

In the embodiments of FIGS. 8C and 8D, the COB packaged white lightemitting devices 820 comprises a plurality (array) of CSP LEDscomprising the first photoluminescence layer 832 that are mounted on thesubstrate (board) 824. The second photoluminescence layer 834 isconstituted by filling the volume 828 contained within the peripheralwall 826 with a light transmissive material (optical encapsulant)containing the second photoluminescence material. In the embodiments ofFIGS. 8E and 8F, the COB packaged white light emitting devices 820comprises a plurality (array) of CSP LEDs mounted on the substrate(board) 824. Since the CSP LEDs include both first and secondphotoluminescence layers 832, 834, there is no need for a peripheralwall or light transmissive optical encapsulant. However, in otherembodiments, a peripheral wall and optical encapsulant can be providedto provide environmental protection to the CSP LEDs.

CSP (Chip Scale Packaged) Light Emitting Devices

FIGS. 9A and 9B show side views of CSP light emitting devices 920 inaccordance with embodiments of the invention. In each embodiment, afirst photoluminescence layer 932 comprising a manganese-activatedfluoride photoluminescence material is applied (deposited) as a uniformthickness layer directly onto and covers at least the principle (e.g.top) light emitting face of a blue LED flip chip (die) 930.

As shown in FIG. 9A, a second photoluminescence material layer 934comprising, for example, a cerium-activated yellow garnet phosphorhaving a general composition Y₃(Al,Ga)₅O₁₂:Ce is applied (deposited) asa uniform thickness layer onto and covers the first photoluminescencelayer 932.

As illustrated in FIG. 9B, the LED chip 930 has uniform thickness firstand second photoluminescence layers 932, 934 applied to the lightemitting top face (top as shown) and four light emitting side faces andcan be in the form of a conformal coating.

FIGS. 9C and 9D show side views of CSP light emitting devices 920 inaccordance with embodiments of the invention. In each embodiment, afirst photoluminescence layer 932 comprising a manganese-activatedfluoride photoluminescence material covers (is applied to) the top lightemitting face of a blue LED flip chip 930 and a light reflectivematerial 942 covers the light emitting side faces. The light reflectivematerial can comprise a white material such as a white silicone materialor alike. The light reflective material layer 942 ensures that all bluelight generated by light emitting side faces of the LED chip 930 passesinto the first photoluminescence layer 932 comprising amanganese-activated fluoride photoluminescence material. This can be ofparticular benefit for devices that are configured to generate lower CCT(warm light) light, for example up to 3000K, which require a greaterproportion of red light to achieve the desired color temperature. Inthis way, the inclusion of a light reflective material 942 thatsubstantially covers the light emitting side faces of the LED chip 930can lessen a need of having to include more manganese-activated fluoridephotoluminescence material in the photoluminescence layer to compensatefor a “dilution” effect by cooler white created by the emission of bluelight from the light emitting side faces of the LED chip. That is, theblue light emission from the light emitting side faces of the LED chipcan necessitate more manganese-activated fluoride photoluminescencematerial usage in the photoluminescence layer to generate the desiredlower CCT (warm light) light, for example up to 3000K. A desired warmercolor temperature can thus be attained without using moremanganese-activated fluoride photoluminescence material in thephotoluminescence layer due to the inclusion of a light reflectivematerial that substantially covers the light emitting side faces of theLED chip. Since manganese-activated fluoride photoluminescence materialis significantly more expensive than other types of photoluminescencematerials (for example, green/yellow garnet-based phosphors), reducingthe amount of manganese-activated fluoride photoluminescence material toattain a desired color temperature (warm) by using a relativelyinexpensive light reflective material in this way provides a significantcost saving and makes the invention more cost effective and economicalto manufacture the light emitting device.

A further benefit of having a light reflective material layer that atleast substantially covers the light emitting side faces of the LED chipis that this may lead to a more uniform color and uniform color overangle of emitted light.

In the embodiment of FIG. 9C, the CSP light emitting device 920comprises a first photoluminescence layer 932, comprising in terms ofphotoluminescence material only a manganese-activated fluoridephotoluminescence material, that is applied (deposited) as a uniformthickness layer directly onto the light emitting top face (top face asshown) of a blue LED flip chip 930. Optionally, as indicated in FIG. 9Cthe first photoluminescence layer 932 may be provided on a lighttransmissive substrate 944 (indicated by a dashed line) such as a glasssubstrate or light transmissive polymer film. Since the firstphotoluminescence layer can be of a thickness 20 μm to 300 μm, a benefitof depositing/fabricating the first photoluminescence layer on asubstrate can be ease of manufacture when manufacturing the firstphotoluminescence layer as a separate component and then applying thisto the LED chip. A further benefit of the substrate is that this canprovide environmental protection to the first photoluminescence layer.The CSP light emitting device 920 further comprises a light reflectivematerial 942 that covers the light emitting side faces of the LED flipchip 930 and constitute a light reflective enclosure (cup) around theperiphery of the LED flip chip 930. The light reflective material 942reflects light that would otherwise be emitted from the side faces ofthe LED chip back into the LED chip 932 and this light is eventuallyemitted from the LED chip through the top light emitting face. As can beseen FIG. 9C, the first photoluminescence layer 932 completely coversthe top surface of the LED chip 930 and the light reflective material942 thereby ensuring that all light generated by the CSP light emittingdevice 920 is emitted through the first photoluminescence layer 932.

The CSP light emitting device 920 of FIG. 9D is the same as that of FIG.9C except that it further comprises a second photoluminescence layer 934that is in contact with and covers the first photoluminescence layer932. Optionally, as indicated in FIG. 9D the photoluminescence layers932, 934 may be provided on a light transmissive substrate 944(indicated by a dashed line) such as a glass substrate or lighttransmissive polymer film. Since the photoluminescence layers may bethin, a benefit of depositing/fabricating the photoluminescence layerson a substrate can be ease of manufacture when manufacturing thephotoluminescence layers as a separate component and then applying thisto the LED chip. A further benefit of the substrate is that this canprovide environmental protection to the photoluminescence layers.

FIGS. 9E to 9K illustrate a method of manufacture of the CSP white lightemitting device 920 of FIG. 9D.

First, as shown in FIG. 9E, a photoluminescence component (film) 946 isprovided comprising the first and second photoluminescence layers 932,934. The photoluminescence film 946 can be manufactured by for exampleextrusion, slot die coating or screen printing. As described herein, thephotoluminescence layers 932, 934 may be provided on a lighttransmissive substrate 944 (not shown) such as a glass substrate orlight transmissive polymer film.

Next, with the first photoluminescence layer 932 oriented uppermost, ameasured quantity of a light transmissive material 948, such as acurable silicone optical encapsulant, is dispensed on the firstphotoluminescence layer 932 at predetermined locations (FIG. 9F). Tomaximize device yield from the photoluminescence film 946 the locationsmay, as illustrated, comprise a square array of rows and columns.

An LED flip chip 930, with its light emitting face 950 facing thephotoluminescence film (i.e. base 940 uppermost), is placed on arespective optical encapsulant 948 and pushed into the opticalencapsulant 948. The encapsulant 948 bonds the LED chip tophotoluminescence film and forms a thin optical coupling layer betweenthe first photoluminescence 932 and the top light emitting face 950 ofthe LED chip 930.

As indicated in FIG. 911 , there is a square lattice of valleys 952between rows and columns of LED dies 930. The valleys 952 are filledwith a light reflective material 942 such as a for example a whitesilicone material (FIG. 91 ).

Finally, as shown in FIG. 9J, individual CSP devices 920 are produced bycutting along cut lines 954. The cut individual CSP devices 920 can beseen in FIG. 9K.

It will be appreciated that a similar method can be used to manufacturethe CSP white light emitting device 920 of FIG. 9C using aphotoluminescence film comprising only a first photoluminescence layer932.

FIGS. 9L and 9M show side views of CSP light emitting devices 920 inaccordance with embodiments of the invention. In each embodiment, afirst photoluminescence layer 932 comprising a manganese-activatedfluoride photoluminescence material covers (is applied to) the top lightemitting face of a blue LED chip 930, there is a light transmissiveregion 956 around the periphery of the LED chip 930 and a lightreflective material 942 that covers the light transmissive region 956and the light emitting side faces of the LED chip. It is to be notedthat the first photoluminescence layer 932 extends beyond the lightemitting top face of the LED chip and covers at least the lighttransmissive region 956 and may as indicated in the figures additionallycover the light reflective region 956. The light reflective material cancomprise a white material such as a white silicone material.

The light reflective material layer 942 ensures that all blue lightgenerated by light emitting side faces of the LED chip 930 passes intothe first photoluminescence layer 932 comprising a manganese-activatedfluoride photoluminescence material. The light transmissive region 956increases the amount of blue light generated by light emitting sidefaces of the LED chip 930 that reaches the first photoluminescence layer932. As described herein, this can be of particular benefit for devicesthat are configured to generate lower CCT (warm light) light, forexample up to 3000K, which require a greater proportion of red light toachieve the desired color temperature.

In this way, the inclusion of a light reflective material 942 incombination with the light transmissive portion (layer) 956 that atleast substantially covers the light emitting side faces of the LED chip930 can lessen a need of having to include more manganese-activatedfluoride photoluminescence material in the photoluminescence layer tocompensate for a “dilution” effect by cooler white created by theemission of blue light from the light emitting side faces of the LEDchip. That is, the blue light emission from the light emitting sidefaces of the LED chip can necessitate more manganese-activated fluoridephotoluminescence material usage in the photoluminescence layer togenerate the desired lower CCT (warm light) light, for example up to3000K. A desired warmer color temperature can thus be attained withoutusing more manganese-activated fluoride photoluminescence material inthe photoluminescence layer due to the inclusion of a light reflectivematerial that substantially covers the light emitting side faces of theLED chip. Since manganese-activated fluoride photoluminescence materialis significantly more expensive than other types of photoluminescencematerials (for example, green/yellow garnet-based phosphors), reducingthe amount of manganese-activated fluoride photoluminescence material toattain a desired color temperature (warm) by using a relativelyinexpensive light reflective material in this way provides a significantcost saving and makes the invention more cost effective and economicalto manufacture the light emitting device.

In the embodiment of FIG. 9L, the CSP light emitting device 920comprises a first photoluminescence layer 932, comprising in terms ofphotoluminescence material only a manganese-activated fluoridephotoluminescence material, that can be applied (deposited) as a uniformthickness layer directly onto the light emitting face (top face asshown) of a blue LED flip chip 930. The light emitting device furthercomprises a light transmissive portion (layer) 956 applied to each ofthe four light emitting side faces of the LED chip and has a form whichextends upwardly and outwardly from the base 940 of the LED chip. Thelight transmissive portion 956 defines a light transmissive regionaround the periphery of the LED chip and allows light emitted from thesides faces of the LED chip to travel to the first photoluminescencelayer 932. The CSP light emitting device 920 further comprises a lightreflective material 942 in contact with the light transmissive regionwhich extends upwardly and inwardly from the base 940 of the LED chipand defines a light reflective enclosure (cup) around the periphery ofthe light transmissive portion 956. The light reflective portion 942reflects light emitted from the side faces of the LED die in an upwarddirection towards the first photoluminescence layer 932. As can be seenFIG. 9L, the first photoluminescence layer 932 completely covers the topsurface of the LED die 930, light transmissive portion 956, and lightreflective portion 942 thereby ensuring that all light generated by theCSP light emitting device 920 is emitted through the firstphotoluminescence layer 932.

The CSP light emitting device 920 of FIG. 9M is the same as that of FIG.9L except that it further comprises a second photoluminescence layer 934that is in contact with and covers the first photoluminescence layer932.

FIGS. 9N to 9T illustrate a method of manufacture of the CSP white lightemitting device 920 of FIG. 9M.

First, as shown in FIG. 9N, a photoluminescence film 946 is providedcomprising the first and second photoluminescence layers 932, 934. Thephotoluminescence film 946 can be manufactured by for example extrusion,slot die coating or screen printing. As described herein, thephotoluminescence layers 932, 934 may be provided on a lighttransmissive substrate 944 (not shown) such as a glass substrate orlight transmissive polymer film.

Next, with the first photoluminescence layer 932 oriented uppermost, ameasured quantity of a light transmissive material 956, such as acurable silicone optical encapsulant, is dispensed on the firstphotoluminescence layer 932 at predetermined locations (FIG. 9O). Tomaximize device yield from the photoluminescence film 946 the locationsmay, as illustrated, comprise a square array of rows and columns.

An LED flip chip 930, with its light emitting face 950 facing thephotoluminescence film (i.e. base 940 uppermost), is placed on arespective optical encapsulant 956 and pushed into the opticalencapsulant 956 (FIG. 9P). The encapsulant 956 forms a concave meniscusthat extends up and covers each of the light emitting side faces of theLED dies as shown in FIG. 9Q.

As indicated in FIG. 9Q, there is a square lattice of valleys 952between rows and columns of LED dies 930. The valleys 952 are filledwith a light reflective material 942 such as a for example a whitesilicone material (FIG. 9R).

Finally, as shown in FIG. 9S, individual CSP devices 920 are produced bycutting along cut lines 954. The cut individual CSP devices 920 can beseen in FIG. 9T.

It will be appreciated that a similar method can be used to manufacturethe CSP white light emitting device 920 of FIG. 9L using aphotoluminescence film comprising only a first photoluminescence layer932.

The light emitting devices 920 of FIGS. 9A to 9D, 9L and 9M function andexhibit the same advantages as discussed in relation the light emittingdevice of FIG. 2 for example. Hence, the statements made in relation toFIG. 2 apply equally to the embodiment of FIGS. 9A to 9D, 9L and 9M.

Experimental Test Data

In this specification, the following nomenclature is used to denotewhite light emitting devices: Com. # denotes a comparative (known) whitelight emitting device comprising a single-phosphor layer and Dev. #denotes a two-phosphor layer white light emitting device in accordancewith an embodiment of the invention.

Comparative white light emitting devices (Com. #) and white lightemitting devices in accordance with the invention (Dev. #) each compriseSMD 2835 packaged devices containing three serially connected 1133 (11mil×33 mil) blue LED chips of dominant wavelength λ_(d)≈455 nm. Eachdevice is a nominal 0.9 W (Drive The rated driving condition is 100 mAand a forward drive voltage V_(f) of 9 V) device and is intended togenerate white light with a target Correlated Color Temperature (CCT) of2700K and a general color rendering index CRI Ra>90.

The phosphors used in the test devices are KSF (K₂SiF₆:Mn⁴⁺) fromIntematix Corporation, green YAG phosphor (Intematix NYAG4156—(Y,Ba)_(3-x)(Al_(1-y)Ga_(y))₅O₁₂:Ce_(x) Peak emission wavelength λ_(pe)=550nm) and CASN (Ca_(1-x)Sr_(x)AlSiN₃:Eu λ_(pe)≈615 nm). The CASN isincluded to achieve the 2700K color target and general CRI Ra>90.

For the single-layer comparative devices, Com. #, the three phosphors(KSF, YAG and CASN) were mixed in a phenyl silicone and the mixturedispensed into the 2835 package to fill the cavity. The single-phosphorlayer is then cured in an oven.

For the two-layer devices (Dev. #): KSF phosphor is mixed into a phenylsilicone and dispensed into the 2835 package to partially fill the LEDcavity. The KSF phosphor layer is cured in an oven. YAG phosphor ismixed with a phenyl silicone and then dispensed on top of KSF layer tofully fill the LED cavity and the cured in an oven. The KSF phosphorlayer can additionally include CASN and/or YAG.

Experimental Test Data—Optical Performance

The test method involves measuring total light emission of the packagedwhite light emitting devices in an integrating sphere.

TABLE 1 tabulates phosphor composition of a comparative device Com.1(single-layer device) and a two-layer device Dev.1 in accordance withthe invention. TABLE 2 tabulates total phosphor usage for thesingle-layer device (Com.1) and the two-layer device (Dev.1). Thephosphor weight values (weight) in TABLES 1 and 2 are normalized to theweight of KSF in the single phosphor layer of comparative device Com.1.

As can be seen from TABLE 1, in terms of phosphor composition: Com. 1comprises a single phosphor layer comprising a mixture of 69.9 wt %(weight=1.000) KSF, 28.1 wt % (weight=0.400) YAG and 2.1 wt %(weight=0.030) CASN. Dev.1 comprises a two-layered phosphor structurehaving a 1^(st) phosphor layer comprising a mixture of 95.2 wt %(weight=0.457) KSF and 4.8 wt % (weight=0.023) CASN and a 2^(nd)phosphor layer comprising 100.0 wt % (weight=0.561) YAG.

TABLE 1 Phosphor composition of a single-layer LED (Com.1) and atwo-layer LED (Dev.1) 1^(st) phosphor layer 2^(nd) phosphor layer KSFYAG CASN YAG CASN Device weight¹ wt %² weight¹ wt %² weight¹ wt %²weight¹ wt %² weight¹ wt %² Com.1 1.000 69.9 0.400 28.0 0.030 2.1 — — —— Dev.1 0.457 95.2 — — 0.023 4.8 0.561 100.0 — — ¹weight-phosphor weightnormalized to weight of KSF of single phosphor layer of comparativedevice (Com.1) ²wt %-phosphor weight percentage of total phosphorcontent of the layer

TABLE 2 Phosphor usage of a single-layer LED (Com.1) and a two-layer LED(Dev.1) Phosphor usage KSF YAG CASN TOTAL Device weight¹ % wt %³ weight¹% wt %³ weight¹ % wt %³ weight¹ Com.1 1.000 100.0 69.9 0.400 100.0 28.00.030 100 2.1 1.430 Dev.1 0.457 46.0 43.9 0.561 129.0 53.9 0.023 76 2.21.041 ¹weight-phosphor weight normalized to weight of KSF of singlephosphor layer of comparative device (Com.1) ³wt %-phosphor weightpercentage of total phosphor content of device

TABLE 3 tabulates the measured optical performance of the light emittingdevices Com.1 and Dev.1. As can be seen from TABLE 3 the color point oflight generated by the devices are very similar with the flux generatedby the two layer-device of the invention (Dev.1) being 4.1 lm greater(3.4% brighter: Brightness—Br) than the single-layer comparative device(Com.1). However, as can be seen from TABLE 2, compared with thesingle-layer device Com.1, KSF usage of the two-layer device Dev.1 inaccordance with the invention is reduced from a normalized weight(weight) 1.000 to 0.457, that is a 54% reduction in KSF usage comparedwith Com.1. Moreover, CASN usage of the two-layer device Dev.1 is alsoreduced from a normalized weight 0.030 to 0.023, that is a 24% reductionin CASN usage compared with Com.1. While there is an increase of 29%(0.561 from 0.400) in YAG usage, total phosphor usage is reduced fromweight=1.430 to 1.041, that is a reduction of 28% total phosphor usage.As noted above, YAG is inexpensive compared with both KSF (typically1/100 to 1/150 of the cost) and CASN (typically at least 1/20 of thecost). Consequently, since YAG is a fraction of the cost of KSF or CASN,the overall cost of the device is dramatically reduced in this way. Aswell as the cost saving afforded by the reduction in KSF and CASNcontent, two-layer devices in accordance with the invention are easierto manufacture as they use less total phosphor material which means thatthe phosphor material loading in silicone is reduced and this reductioncan increase the reliability/stability of the dispensing process.

It is believed that the reason for the increase in YAG usage is that dueto less blue excitation light reaching the 2^(nd) phosphor layer, moreYAG phosphor is required to generate green light to attain the selectedcolor target. As discussed above, it is believed that since the KSFlayer contains substantially only KSF (individual KSF layer), KSF usageis reduced, because the KSF can absorb blue excitation light withouthaving to compete with the YAG phosphor as is the case in the knownsingle-layer devices comprising a single layer having a mixture ofphosphors.

TABLE 3 Measured optical performance of a single-layer device (Com.1)and a two-layer device (Dev.1) CIE CRI Device x y Flux (lm) Br (%) RaΔRa R9 ΔR9 Com.1 0.4544 0.4183 121.7 100.0 90.3 0.0 57.6 0.0 Dev.10.4548 0.4208 125.8 103.4 90.9 0.6 57.4 −0.2

TABLE 4 tabulates phosphor composition of a comparative device Com.2(single-layer device) and two-layer devices Dev.2 to Dev.5 in accordancewith the invention for increasing proportion (wt %) of KSF in the 1^(st)phosphor layer. TABLE 5 tabulates total phosphor usage for thesingle-layer device (Com.2) and the two-layer devices (Dev.2 to Dev.5).The phosphor weights in TABLES 4 and 5 are normalized to the weight ofKSF in the comparative device Com.2.

As can be seen from TABLE 4, in terms of phosphor composition: Com.2comprises a single phosphor layer comprising a mixture of 68.9 wt %(weight=1.000) KSF, 29.0 wt % (weight=0.421) YAG and 2.1 wt %(weight=0.031) CASN. Devices Dev.2 to Dev.5 comprise a 1^(st) phosphorlayer having an increasing proportion (wt %) of KSF in the 1^(st)phosphor layer (76.8 wt % to 100 wt %). More specifically: Dev.2comprises a two-layered structure having a 1^(st) phosphor layercomprising a mixture of 76.8 wt % (weight=0.770) KSF, 3.2 wt %(weight=0.032) CASN and 20.0 wt % (weight=0.200) YAG, and a 2^(nd)phosphor layer comprising 100.0 wt % YAG (weight=0.345); Dev.3 comprisesa two-layered structure having a 1^(st) phosphor layer comprising amixture of 86.4 wt % (weight=0.665) KSF, 3.6 wt % (weight=0.028) CASNand 10.0 wt % (weight=0.077) YAG and a 2^(nd) phosphor layer comprising100.0 wt % YAG (weight=0.506); Dev.4 comprises a two-layered structurehaving a 1^(st) phosphor layer comprising a mixture of 96.0 wt %(weight=0.639) KSF, 4.0 wt % (weight=0.0270) CASN and a 2^(nd) phosphorlayer comprising 100.0 wt % YAG (weight=0.580); and Dev.5 comprises atwo-layered structure having a 1^(st) phosphor layer comprising 100.0 wt% (weight=0.551) KSF and a 2^(nd) phosphor layer comprising a mixture of96.0 wt % YAG (weight=0.595) and 4.0 wt % (weight=0.025) CASN.

TABLE 4 Phosphor composition of a single-layer LED (Com.2) and two-layerLEDs (Dev.2 to Dev.5) with increasing wt % KSF content in 1^(st) layer1^(st) phosphor layer 2^(nd) phosphor layer KSF YAG CASN YAG CASN Deviceweight¹ wt %² weight¹ wt %² weight¹ wt %² weight¹ wt %² %⁴ weight¹ wt %²Com.2 1.000 68.9 0.421 29.0 0.031 2.1 — — — — — Dev.2 0.770 76.8 0.20020.0 0.032 3.2 0.345 100.0 63.3 — — Dev.3 0.665 86.4 0.077 10.0 0.0283.6 0.506 100.0 86.8 — — Dev.4 0.639 96.0 — — 0.027 4.0 0.580 100.0100.0 — — Dev.5 0.551 100.0 — — — — 0.595 96.0 100.0 0.025 4.0¹weight-phosphor weight normalized to weight of KSF of single phosphorlayer of comparative device (Com.1) ²wt %-phosphor weight percentage oftotal phosphor content of the layer ⁴%-percentage of total YAG contentin 2^(nd) phosphor layer

TABLE 5 Phosphor usage of a single-layer LED (Com.1) and a two-layer LED(Dev.1) Phosphor usage KSF YAG CASN TOTAL Device weight¹ % wt %³ weight¹% wt %³ weight¹ % wt %³ weight¹ Com.2 1.000 100 40.3 0.715 100 28.80.052 100 30.9 2.482 Dev.2 0.770 77 44.0 0.925 129 52.9 0.054 104 3.11.749 Dev.3 0.665 67 39.1 0.990 138 58.1 0.047 90 2.8 1.702 Dev.4 0.63964 38.2 0.985 138 59.0 0.045 87 2.7 1.669 Dev.5 0.551 55 34.4 1.009 14163.0 0.042 81 2.6 1.602 ¹weight-phosphor weight normalized to weight ofKSF of single phosphor layer of comparative device (Com.1) ³wt%-phosphor weight percentage of total phosphor content of device

TABLE 6 tabulates the measured optical performance of the light emittingdevices Com.2 and Dev.2 to Dev.5. As can be seen from TABLE 6 theoptical performance/color point of the devices are very similar with theflux generated by the two layer-devices of the invention (Dev.2 toDev.5) being between about 0.7% and 2.0% brighter (Brightness—Br) thanthe single-layer comparative device (Com.2). However, as can be seenfrom TABLE 5, compared with the single-layer device Com.2, KSF usage ofthe two-layer devices Dev.2 to Dev.5 in accordance with the invention isreduced by 23% up to 45% depending on the proportion (wt %) of KSF inthe 1^(st) phosphor layer. It will be noted from TABLE 5 that thegreatest reduction in KSF usage is when the 1^(st) phosphor layer, interms of total phosphor content of the layer, exclusively comprises KSF(i.e. Dev.5-100 wt % KSF in 1^(st) phosphor layer). This being said, itwill be appreciated that even for a device having about a 75% wt %proportion of KSF of a total phosphor content in the 1^(st) phosphorlayer (Dev.2), the saving in KSF usage is still about 25% which issubstantial when the high cost of KSF is taken into account, resultingin nearly a 25% reduction in the overall cost of the manufacturing ofthe device.

As evidenced in TABLE 5, increasing the proportion (wt %) of KSF in the1^(st) phosphor layer has the effect of (i) reducing KSF usage (23% to45%), (ii) reducing CASN usage, (iii) increasing YAG usage, and (iv)reducing total phosphor usage. These effects together provide asignificant cost reduction.

It will be further noted that in devices in accordance with theinvention, the 2^(nd) phosphor layer can comprise from about 60% (Dev.2)to 100% (Devs.4 and 5) YAG (green photoluminescence material) of thetotal YAG content of the device.

TABLE 6 Optical performance of single-layer LED (Com.2) and two-layerLEDs (Dev.2 to Dev.5) CIE CCT Flux LE Br CRI Device x y (K) (lm) (lm/W)(%) Ra ΔRa R9 ΔR9 Com.2 0.4591 0.4169 2759 110.1 345.4 100.0 93.5 0.065.5 0.0 Dev.2 0.4591 0.4173 2763 111.2 347.2 100.9 92.5 −1.0 61.4 −4.1Dev.3 0.4587 0.4170 2767 111.7 345.8 101.4 93.0 −0.5 64.1 −1.4 Dev.40.4589 0.4175 2766 110.9 345.3 100.7 93.5 0.0 67.5 2.0 Dev.5 0.45990.4135 2722 112.8 341.7 102.4 94.8 1.3 79.0 13.5

Experimental Test Data—Thermal Performance

TABLE 7 tabulates the thermal stability of the single-layer lightemitting device Com.1 and two-layer light emitting device Dev. 1. As canbe seen from TABLE 7, compared with the single-layer device Com.1, thetwo-layer devices Dev.1 in accordance with the invention exhibitsgreater thermal stability in terms of light emission and emission colorstability.

For example, the average flux generated by Dev.1 drops 12.3% (116.5 lmto 102.1 lm) when operated at 85° C. (H) compared with being operated at25° C. (C). In comparison the average flux generated by Com.1 drops12.7% (From 115.9 lm to 101.2 lm) when operated at 85° C. (H) comparedwith being operated at 25° C. (C).

In terms of luminous efficacy (LE), the average value of LE of Dev.1drops 10.4% (From 123.1 lm/W to 110.4 lm/W) when operated at 85° C. (H)compared with being operated at 25° C. (C). In comparison, the averagevalue of LE of Com.1 drops 11.6% (From 122.9 lm/W to 108.6 lm/W) whenoperated at 85° C. (H) compared with being operated at 25° C. (C). Thisdemonstrates the superior thermal stability of a device formed inaccordance with the invention since the drop in average LE of 10.4%(Dev.1) is less than the drop of 11.6% (Com.1).

In terms of general color rendering index CRI Ra, the average value ofCRI Ra of Dev.1 increases by an amount of only 1.5 (From 93.2 to 95.2)when operated at 85° C. (H) compared with being operated at 25° C. (C).In comparison, the average value of CRI Ra of Com.1 increases by anamount 2.0 (From 91.2 to 93.3) when operated at 85° C. (H) compared withbeing operated at 25° C. (C). This demonstrates the superior thermalstability of a device formed in accordance with the invention since theincrease of average CRI Ra of 1.5 (Dev.1) is less than the increase of2.0 (Com.1).

In terms of color rendering index CRI R8, the average value of CRI R8 ofDev.1 increases by an amount of only 0.6 (From 97.1 to 97.7) whenoperated at 85° C. (H) compared with being operated at 25° C. (C). Incomparison, the average value of CRI R8 of Com.1 increases by an amount1.2 (From 82.6 to 83.9) when operated at 85° C. (H) compared with beingoperated at 25° C. (C). This demonstrates the superior thermal stabilityof a device formed in accordance with the invention since the increaseof average CRI R8 of 0.6 (Dev.1) is less than the increase of 1.2(Com.1).

In terms of color rendering index CRI R9, the average value of CRI R9 ofDev.1 increases by an amount of only 2.3 (From 83.3 to 85.5) whenoperated at 85° C. (H) compared with being operated at 25° C. (C). Incomparison, the average value of CRI R9 of Com.1 increases by an amount5.7 (From 57.4 to 63.1) when operated at 85° C. (H) compared with beingoperated at 25° C. (C). This demonstrates the superior thermal stabilityof a device formed in accordance with the invention since the increaseof average CRI R9 of 2.3 (Dev.1) is less than the increase of 5.7(Com.1).

TABLE 7 Thermal stability of a single-layer LED (Com.1) and two-layerLED (Dev. 1) Flux LE CIE CRI Device Condition (lm) (lm/W) x y Ra R8 R9Com.1 Cold (C) 25° C. 115.0 123.2 0.4542 0.4073 91.0 82.4 57.0 117.3119.8 0.4534 0.4083 91.3 82.5 57.3 115.4 125.6 0.4523 0.4101 91.4 83.057.8 Average 115.9 122.9 0.4533 0.4086 91.2 82.6 57.4 Hot (H) 100.4107.1 0.4579 0.3985 92.9 83.4 62.2 85° C. 102.9 109.6 0.4570 0.3991 93.483.9 63.2 100.2 109.1 0.4562 0.4008 93.5 84.4 63.9 Average 101.2 108.60.4570 0.3995 93.3 83.9 63.1 Δ C to H −12.7% −13.1% 0.0037 −0.0088 1.91.0 5.2 −12.3%  −8.5% 0.0036 −0.0092 2.1 1.4 5.9 −13.2% −13.1% 0.0039−0.0093 2.1 1.4 6.1 Average −12.7% −11.6% 0.0040 −0.0090 2.0 1.2 5.7Dev.1 Cold (C) 25° C. 118.5 125.0 0.4456 0.4322 92.7 96.0 79.4 116.7126.2 0.4467 0.4298 93.6 96.8 81.7 114.4 118.2 0.4512 0.4265 94.7 98.488.9 Average 116.5 123.1 0.4478 0.4295 93.4 97.1 83.3 Hot (H) 85° C.103.9 112.3 0.4495 0.4242 94.5 96.7 82.1 102.3 112.1 0.4505 0.4216 95.497.3 84.2 100.2 106.8 0.4553 0.4182 95.7 99.0 90.5 Average 102.1 110.40.4502 0.4213 95.2 97.7 85.6 Δ C to H −12.3% −10.1% 0.0039 −0.0080 1.80.7 2.7 −12.3% −11.3% 0.0038 −0.0082 1.8 0.5 2.5 −12.4%  −9.7% 0.0041−0.0083 1.0 0.6 1.6 Average −12.3% −10.4% 0.0040 −0.0080 1.5 0.6 2.3

The reliability, relative brightness, of a light emitting device inaccordance with the invention (Dev.1) comprising two-layers is comparedwith the reliability of a known device (Com.1) comprising a single-layerof mixed photoluminescence materials under Wet High TemperatureOperation Life test condition (WHTOL), temperature is 85° C., relativehumidity is 85%. The driving condition is 9V and 120 mA. As shown inFIG. 10 , the two-layer LED's (Dev.1) relative intensity at 336 hrs is96.4% while the relative intensity of the known single-layer LED(Com. 1) dropped to 91.45% at 336 hrs. It is believed that thisimprovement in reliability is due to a combination of the reduced usageof KSF phosphor as discussed above and the protection provided by the2^(nd) photoluminescence layer covering the manganese-activated fluoridephotoluminescence layer (1^(st) layer).

Another accelerated reliability is a water boiling test. In this test,the LEDs were immersed in 85° C. deionized water for 4 hours. The LEDbrightness is tested before and after immersion in water. The results ofthis test are tabulated in TABLE 8. Under these conditions, it isbelieved that hot water may penetrate the upper photoluminescence layersilicone surface to react with Fluoride photoluminescence material. Thetwo-layer device of the invention provides increased isolation betweenwater and the KSF (manganese-activated fluoride photoluminescencematerial) in the 1^(st) phosphor layer, resulting in better lumenmaintenance than the single-layer device.

TABLE 8 Relative brightness of single-layer LEDs (Com.1) andtwo-single-layer LEDs (Dev.1) under immersion in boiling water (85° C.)for 4 hours Relative Brightness (%) after 4 hours Sample number Device 12 3 4 5 6 7 8 9 10 max min avg Com.1 95.4 96.4 96.7 93.9 94.7 96.1 93.594.1 93.0 94.6 96.7 93.0 94.8 Dev.1 97.3 97.1 97.5 97.6 98.0 98.3 98.298.0 98.4 97.3 98.4 97.1 97.8

Experimental Data—Packaged White Light Emitting Devices Utilizing CSPLEDs

TABLE 9 tabulates the measured optical performance of packaged whitelight emitting devices Devs. 6 to 8 that utilize CSP LEDs.

Dev.6 has the packaging arrangement of FIG. 5D and comprises a 2835package containing a 4343 (43 mil×43 mil≈1.1 mm²) CSP flip chip LED ofdominant wavelength λ_(d)≈455 nm. The LED flip chip has a singlephotoluminescence layer which in terms of photoluminescence material(phosphor) consists of only KSF applied to its top light emitting faceonly. The photoluminescence layer is provided on a glass substrate. Thepackage cavity is filled with a light reflective white silicone to alevel that at least substantially or completely covers the side faces ofthe LED chip without covering the glass substrate. The remainder of thecavity is filled with silicone containing a mixture of broadband greento red emitting photoluminescence materials. The device is a nominal 0.3W (rated driving condition is 120 mA and a forward drive voltage of 2.75V) device and is intended to generate white light with a targetCorrelated Color Temperature (CCT) of 2700K and a general colorrendering index CRI Ra≥90 and a CRI R9 of at least 50.

Dev.7 has the packaging arrangement of FIG. 5F and comprises a 2835package containing a 4343 (43 mil×43 mil≈1.1 mm²) CSP flip chip LED ofdominant wavelength λ_(d)≈455 nm. The LED flip chip has a singlephotoluminescence layer which in terms of photoluminescence material(phosphor) consists of only KSF applied to its top light emitting faceonly. The photoluminescence layer is provided on a glass substrate. TheCSP LED further comprises light reflective material that covers the fourlight emitting side faces of the LED chip. The package cavity is filledwith silicone containing a mixture of broadband green to red emittingphotoluminescence materials. The device is a nominal 0.3 W (rateddriving condition is 120 mA and a forward drive voltage of 2.75 V)device and is intended to generate white light with a target CorrelatedColor Temperature (CCT) of 2700K and a general color rendering index CRIRa≥90 and a CRI R9 of at least 50.

Dev.8 has the packaging arrangement of FIG. 5A and comprises a 2835package containing a 4343 (43 mil×43 mil≈1.1 mm²) CSP flip chip LED ofdominant wavelength λ_(d)≈455 nm. The LED flip chip has a singlephotoluminescence layer which in terms of photoluminescence material(phosphor) consists of only KSF applied to its top light emitting faceonly. The photoluminescence layer is provided on a glass substrate. Thepackage cavity is filed with silicone containing a mixture of broadbandgreen to red emitting photoluminescence materials. The device is anominal 0.3 W (rated driving condition is 120 mA and a forward drivevoltage of 2.75 V) device and is intended to generate white light with atarget Correlated Color Temperature (CCT) of 4000K and a general colorrendering index CRI Ra≥90 and a CRI R9 of at least 50.

TABLE 9 Optical performance of 2700K (Devs.6 and 7) and 4000K (Dev.8)packaged white light emitting device utilizing CSP LEDs I_(F) Flux LECIE CCT CRI Device (mA) V_(F) (V) (lm) (lm/W) x y (K) Ra R9 Dev.6 1202.84 50.7 149 0.4578 0.4213 2811 91.7 57.2 65 2.75 28.5 160 0.45980.4191 2766 93.3 62.1 Dev.7 120 2.80 52.3 155 0.4576 0.4193 2799 92.862.5 65 2.72 29.4 166 0.4598 0.4193 2750 94.2 67.1 Dev.8 120 2.80 67.2204 0.3833 0.3856 3989 89.1 52.8

Color Temperature Tunable White Light Emitting Devices

While the foregoing description has been in relation to fixed colortemperature light emitting devices, embodiments of the invention alsofind utility in color temperature tunable white light emitting devices.Color temperature tunable white light emitting devices according to theinvention comprise first and second LED chips (dies) for generatinglight of first and second different color temperatures. The LED chipsare electrically configured such that electrical power can be appliedindependently to the first and second LED chips enabling colortemperature tuning of light generated by the device. For example, whenelectrical power is provided to only the first LED chip(s) the devicegenerates light of the first color temperature. When electrical power isprovided to only the second LED chip(s) the device generates light ofthe second color temperature. When electrical power is provided to boththe first and second LED chips the device generates light with a colortemperature between the first and second color temperatures. The exactcolor temperature of light generated by the device depends on the ratioof the electrical power provided to the first and second LED chips. Inthe following description, LED chips with a suffix “a” are used toindicate LED chips that generate light of a first color temperature andLED chips with a suffix “b’ are used to indicate LED chips that generatelight of a second different color temperature.

Packaged Color Temperature Tunable White Light Emitting DevicesUtilizing CSP LEDs

FIGS. 11A to 11E are cross sectional side views of packaged colortemperature tunable white light emitting devices 1120 in accordance withembodiments of the invention that utilize CSP (Chip Scale Packaged) LEDs1158.

Each of the color temperature tunable devices 1120 of FIGS. 11A to 11Ccomprise a package 1122, one or more first CSP LEDs 1158 a (indicated bya heavy solid line), one or more second blue LED chips 1130 b, andsecond photoluminescence layer 1134 that covers the first CSP LED(s)1158 a and the second LED chip(s) 1130 b. The one or more first CSP LEDs1158 a comprise a first LED chip 1130 a with a first photoluminescencelayer 1132 that covers at least its light emitting top face. The firstphotoluminescence layer 1132 comprises a manganese-activated fluoridephotoluminescence material only and can be applied in direct contactwith and may be of a substantially uniform thickness.

As shown in FIG. 11A, a color tunable light emitting device 1120comprises a package 1122 with one or more first CSP LEDs 1158 acomprising a first LED chip 1130 a with a first photoluminescence layer1132 covering (applied to) its light emitting top face only. The devicefurther comprises one or more second LED chips 1130 b. A secondphotoluminescence layer 1134 is deposited so as to fill the cavity 1128and cover the first CSP LED(s) 1158 a and cover the second LED chip(s)1130 b. The first CSP LED(s) 1158 a in conjunction with the secondphotoluminescence layer 1134 generate white light of a first colortemperature while the second blue LED chip(s) 1130 b in conjunction withthe second photoluminescence layer 1134 generates white light of asecond different color temperature. Since light generated by the firstCSP LED(s) 1158 a additionally includes red light generated by themanganese-activated fluoride phosphor of the first photoluminescencelayer 1132 it will typically be warmer in color (that is lower in colortemperature) than the light generated by the second LED chip(s) 1130 bwhich includes light generated by the second photoluminescence layer1134 only.

In the color tunable light emitting device 1120 of FIG. 11B the CSPLED(s) 1158 a comprise an LED chip 1130 a with a first photoluminescencelayer 1132 a that covers the light emitting top face and four side lightemitting faces of the first LED chip 1130 a. As indicated the firstphotoluminescence layer can be in the form of a conformal coating.

As shown in FIG. 11C the CSP LED(s) 1150 a comprise the CSP packagingarrangement of FIG. 9L with a first photoluminescence layer 1132 a thatcovers the light emitting top face and four side light emitting faces ofthe first LED chip 1130 a.

The color temperature tunable light emitting devices of FIGS. 11A to 11Ccan be manufactured by mounting the CSP LED(s) 1158 a and second blueLED chip(s) 1130 b to the base (floor) 1124 of the package cavity 1128and then depositing the second photoluminescence layer 1132 so as tofill the volume (cavity) 1128 and cover the CSP LED(s) 1158 a and LEDchip 1130 b.

The color temperature tunable devices of FIGS. 11D and 11E comprise oneor more first CSP LEDs 1158 a that generate white light of a first colortemperature and one or more second CSP LEDs 1158 b that generate whitelight of a second different color temperature. The first and second CSPLEDs 1158 a, 1158 b each respectively comprise an LED chip 1130 a, 1130b with first photoluminescence layer 1132 a, 1132 b applied to at leastits light emitting top face and a second photoluminescence layer 1134 a,1134 b cover the first photoluminescence layer. The first and secondphotoluminescence layers may be of uniform thickness.

As shown in FIG. 11D a color temperature tunable light emitting device1120 comprises a package 1122 with one or more first and second CSP LEDs1158 a, 1158 b. As illustrated, the first and second CSP LEDs 1158 a,1158 b can, as shown, comprise the CSP packaging arrangement of FIG. 9Bcomprising LED chips 1130 a, 1130 b with first and secondphotoluminescence layers 1132, 1134 applied to their light emitting topface and four side light emitting faces in the form of a conformalcoating. Optionally, the package cavity 1128 can be filled with a lighttransmissive material (optical encapsulant) 1138 such as a siliconematerial to provide environment protection to the CSP LEDs 1158 a, 1158b.

In another embodiment, as shown in FIG. 11E, the first and second CSPLED(s) 1158 a, 1158 b can comprise the CSP packaging arrangement of FIG.9M.

The color temperature tunable light emitting devices of FIGS. 11D and11E can be manufactured by first manufacturing the CSP LEDs 1158 a, 1158b, as herein described (FIGS. 9N to 9T), mounting the CSP LEDs to thefloor of the package cavity 1128 and then filling the cavity with alight transmissive material (optical encapsulant) 1138 to provideenvironment protection to the CSP LEDs 1158 a, 1158 b.

COB Color Tunable White Light Emitting Devices Utilizing CSP LEDs

FIGS. 12A to 12E are cross sectional side views of COB (Chip On Board)color temperature tunable white light emitting devices in accordancewith embodiments of the invention that utilize CSP (Chip Scale Packaged)LEDs.

Each of the color temperature tunable devices of FIGS. 12A to 12Ccomprise a substrate 1124, one or more first CSP LEDs 1158 a (indicatedby a heavy solid line), one or more second blue LED chips 1130 b, andsecond photoluminescence layer 1134 that covers the first CSP LED(s)1158 a and the second LED chip(s) 1130 b. The one or more first CSP LEDs1158 a comprise a first LED chip 1130 a with a first photoluminescencelayer 1132 that covers at least its light emitting top face. The firstphotoluminescence layer 1132 comprises a manganese-activated fluoridephotoluminescence material only and can be applied in direct contactwith and may be of a substantially uniform thickness.

In an embodiment, as shown in FIG. 12A, a COB color tunable lightemitting device 1220 comprises a planar substrate (board) 1224 which maytypically comprise a circuit board such as a Metal Core Printed CircuitBoard (MCPCB). An array of first CSP LEDs 1258 a and an array of secondblue LED chips 1230 b are evenly distributed on the substrate 1224. Toensure a uniform emission color of light, the CSP LEDs 1258 a and secondLED chips 1230 b can be interspersed. Each CSP LED 1258 a comprises afirst LED chip 1230 a with a with a uniform thickness firstphotoluminescence layer 1132 a applied to its light emitting top faceonly. The substrate 1224 further comprises about its entire perimeter aperipheral wall 1226 which encloses all the arrays of CSP LEDs 1258 aand LED chips 1230 b and in conjunction with the substrate 1224 define avolume (cavity) 1228. A second photoluminescence layer 1134 is depositedso as to fill the volume 1228 and cover the first CSP LED(s) 1258 a andsecond LED chip(s) 1230 b. The first CSP LED(s) 1258 a in conjunctionwith the second photoluminescence layer 1234 generates white light of afirst color temperature while the second LED chip(s) 1230 b inconjunction with the second photoluminescence layer 1234 generates whitelight of a second different color temperature.

In the color tunable light emitting device 1220 of FIG. 12B the CSPLED(s) 1258 a comprise an LED chip 1230 a with a uniform thickness firstphotoluminescence layer 1232 a applied to its light emitting top faceand four side light emitting faces and is in the form of a conformalcoating.

As shown in FIG. 12C the CSP LED(s) 1250 a can comprise the CSPpackaging arrangement of FIG. 9L.

The COB color temperature tunable light emitting devices of FIGS. 12A to12C can be manufactured by mounting the first CSP LED(s) 1258 a andsecond LED chip(s) 1230 b to the substrate (board) 1224 and thendepositing the second photoluminescence layer 1234 so as to fill thevolume (cavity) 1128 and cover the first CSP LEDs 1258 a and second LEDchips 1130 b.

FIGS. 12D and 12E are cross sectional side views of COB (Chip On Board)color temperature tunable white light emitting devices 1220 that eachcomprise a plurality of first CSP LEDs 1258 a that generate white lightof a first color temperature and a plurality of CSP LEDs 1258 b thatgenerate white light of a second different color temperature. The firstand second CSP LEDs 1158 a, 1158 b each respectively comprise an LEDchip 1130 a, 1130 b with a uniform thickness first photoluminescencelayer 1132 a, 1132 b applied to at least its light emitting top face anda second photoluminescence layer 1134 a, 1134 b cover the firstphotoluminescence layer.

In the embodiment shown in FIG. 12D, a COB color temperature tunablelight emitting device 1220 comprises a substrate (board) 1124 with anarray of first and second CSP LEDs 1258 a, 1258 b. As illustrated, thefirst and second CSP LEDs 1258 a, 1258 b can comprise the CSP packagingarrangement of FIG. 9B comprising LED chips 1230 a, 1230 b with firstand second photoluminescence layers 1232, 1234 applied to their lightemitting top face and four side light emitting faces in the form of aconformal coating. As indicated in FIG. 12D there is no need for aperipheral wall, though a peripheral wall may be provided and the volumewithin the wall filled with a light transmissive material (opticalencapsulant) such as a silicone material to provide environmentalprotection to the first and second CSP LEDs.

In another embodiment, as shown in FIG. 12E, the first and second CSPLED(s) 1258 a, 1258 b can comprise the CSP packaging arrangement of FIG.9M.

The COB color temperature tunable light emitting devices of FIGS. 12Dand 12E can be manufactured by first manufacturing the first and secondCSP LEDs 1258 a, 1258 b as herein described and then mounting them tothe substrate (board) 1224.

As used in this document, both in the description and in the claims, andas customarily used in the art, the words “substantially,”“approximately,” and similar terms of approximation are used to accountfor manufacturing tolerances, manufacturing variations, manufacturingimprecisions, and measurement inaccuracy and imprecision that areinescapable parts of fabricating and operating any mechanism orstructure in the physical world.

While the invention has been described in detail, it will be apparent toone skilled in the art that various changes and modifications can bemade and equivalents employed, without departing from the presentinvention. It is to be understood that the invention is not limited tothe details of construction, the arrangements of components, and/or themethod set forth in the above description or illustrated in thedrawings. Statements in the abstract of this document, and any summarystatements in this document, are merely exemplary; they are not, andcannot be interpreted as, limiting the scope of the claims. Further, thefigures are merely exemplary and not limiting. Topical headings andsubheadings are for the convenience of the reader only. They should notand cannot be construed to have any substantive significance, meaning orinterpretation, and should not and cannot be deemed to indicate that allof the information relating to any particular topic is to be found underor limited to any particular heading or subheading. Therefore, theinvention is not to be restricted or limited except in accordance withthe following claims and their legal equivalents.

LIST OF REFERENCE NUMERALS

-   -   10 Known light emitting device    -   12 Package    -   14 Cavity    -   16 LED die (chip)    -   18 Optical encapsulant    -   #20 Light Emitting Device    -   #22 Package    -   #24 Base    -   #26 Wall    -   #28 Cavity    -   #30 LED chip (die)    -   #32 First Photoluminescence layer    -   #34 Second photoluminescence layer    -   #36 Passivation layer    -   #38 Light transmissive material    -   #40 LED chip base    -   #42 Light reflective material    -   #44 Light transmissive substrate    -   #46 Photoluminescence component (film)    -   #48 Light transmissive material    -   #50 LED chip light emitting face    -   #52 Valleys    -   #54 Cut lines    -   #56 Light transmissive region (layer)    -   #58 CSP LED    -   #=Figure number

1. (canceled)
 2. A light emitting device comprising: a first LEDcomprising a first LED chip for generating light with a wavelength ofmaximum intensity from 440 nm to 470 nm and a first photoluminescencelayer at least partially covering a light emitting face of the first LEDchip; a second LED chip for generating light with a wavelength ofmaximum intensity from 440 nm to 470 nm; and a second photoluminescencelayer covering the first LED and the second LED chip, the secondphotoluminescence layer comprising photoluminescence material forgenerating light with a wavelength of maximum intensity from 500 nm to650 nm, wherein the first photoluminescence layer comprises at least 75weight percent (wt %) of a manganese-activated fluoridephotoluminescence material of a total photoluminescence material contentof the first photoluminescence layer.
 3. The light emitting device ofclaim 2, comprising a substrate, wherein the first LED and second LEDchip are mounted on the substrate.
 4. The light emitting device of claim3, comprising a package defining a cavity having a cavity floor, whereinthe cavity floor comprises the substrate.
 5. The light emitting deviceof claim 4, wherein the cavity is at least partially filled with lightreflective material.
 6. The light emitting device of claim 3, whereinthe substrate comprises at least one of glass and light transmissivepolymer film.
 7. The light emitting device of claim 2, wherein the firstLED comprises a light reflective material for preventing light emissionfrom light emitting side faces of the first LED chip.
 8. The lightemitting device of claim 7, wherein the first LED comprises a lighttransmissive material disposed between the light reflective material andthe light emitting side faces of the first LED chip.
 9. The lightemitting device of claim 2, wherein the first photoluminescence layercovers each light emitting face of the first LED chip.
 10. The lightemitting device of claim 2, wherein the manganese-activated fluoridephotoluminescence material is selected from the group consisting of:K₂SiF₆:Mn⁴⁺, K₂TiF₆:Mn⁴⁺, and K₂GeF₆:Mn⁴⁺.
 11. A light emitting devicecomprising: a first LED for generating light of a first chromaticity;and a second LED for generating light of a second chromaticity; whereinthe first and second LEDs each comprise: an LED chip for generatinglight with a wavelength of maximum intensity from 440 nm to 470 nm; afirst photoluminescence layer that at least partially covers a lightemitting face of the LED chip, said first photoluminescence layercomprising at least 75 weight percent (wt %) of a manganese-activatedfluoride photoluminescence material of a total photoluminescencematerial content of the first photoluminescence layer; a secondphotoluminescence layer comprising photoluminescence material forgenerating light with a wavelength of maximum intensity from 500 nm to650 nm, wherein the second photoluminescence layer covers the firstphotoluminescence layer.
 12. The light emitting device of claim 11,comprising a substrate, wherein the first LED and second LED are mountedon the substrate.
 13. The light emitting device of claim 12, comprisinga package defining a cavity having a cavity floor, wherein the cavityfloor comprises the substrate.
 14. The light emitting device of claim12, wherein the substrate comprises at least one of glass and lighttransmissive polymer film.
 15. The light emitting device of claim 11,wherein at least one of the first and second LEDs comprises a lightreflective material for preventing light emission from light emittingside faces of the LED chip.
 16. The light emitting device of claim 15,wherein the at least one of the first and second LEDs comprises a lighttransmissive material disposed between the light reflective material andthe light emitting side faces of the LED chip.
 16. The light emittingdevice of claim 11, wherein the manganese-activated fluoridephotoluminescence material is selected from the group consisting of:K₂SiF₆:Mn⁴⁺, K₂TiF₆:Mn⁴⁺, and K₂GeF₆:Mn⁴⁺.